In the first dark days of the pandemic, as an Amazon worker named Christian Smalls planned a small, panicked walkout over safety conditions at the retailer’s only fulfillment center in New York City, the company quietly mobilized.

Amazon formed a reaction team involving 10 departments, including its Global Intelligence Program, a security group staffed by many military veterans. The company named an “incident commander” and relied on a “Protest Response Playbook” and “Labor Activity Playbook” to ward off “business disruptions,” according to newly released court documents.

In the end, there were more executives — including 11 vice presidents — who were alerted about the protest than workers who attended it. Amazon’s chief counsel, describing Mr. Smalls as “not smart, or articulate,” in an email mistakenly sent to more than 1,000 people, recommended making him “the face” of efforts to organize workers. The company fired Mr. Smalls, saying he had violated quarantine rules by attending the walkout.

In dismissing and smearing him, the company relied on the hardball tactics that had driven its dominance of the market. But on Friday, he won the first successful unionization effort at any Amazon warehouse in the United States, one of the most significant labor victories in a generation. The company’s response to his tiny initial protest may haunt it for years to come.

Mr. Smalls and his best friend from the warehouse, Derrick Palmer, had set their sights on unionizing after he was forced out. Along with a growing band of colleagues — and no affiliation with a national labor organization — the two men spent the past 11 months going up against Amazon, whose 1.1 million workers in the United States make it the country’s second-largest private employer.

At the bus stop outside the warehouse, a site on Staten Island known as JFK8, they built bonfires to warm colleagues waiting before dawn to go home. They made TikTok videos to reach workers across the city. Mr. Palmer brought homemade baked ziti to the site; others toted empanadas and West African rice dishes to appeal to immigrant workers. They set up signs saying “Free Weed and Food.”

The union spent $120,000 overall, raised through GoFundMe, according to Mr. Smalls. “We started this with nothing, with two tables, two chairs and a tent,” he recalled. Amazon spent more than $4.3 million just on anti-union consultants nationwide last year, according to federal filings.

The unionization vote reflects an era of rising worker power. In recent months, a string of Starbucks stores have voted to organize as well. But JFK8, with 8,000 workers, is one of Amazon’s signature warehouses, its most important pipeline to its most important market.

Amazon has fought unionization for years, considering it a dire threat to its business model. Its ability to speed packages to consumers is built on a vast chain of manual labor that is monitored down to the second. No one knows what will happen if the newly organized workers try to change that model or disrupt operations — or if their union is replicated among the more than 1,000 Amazon fulfillment centers and other facilities across the country.

For all their David-versus-Goliath disadvantages, the Staten Island organizers had the cultural moment on their side. They were buoyed by a tightened labor market, a reckoning over what employers owe their workers and a National Labor Relations Board emboldened under President Biden, which made a key decision in their favor. The homegrown, low-budget push by their independent Amazon Labor Union outperformed traditional labor organizers who failed at unionizing Amazon from the outside, most recently in Bessemer, Ala.

“I think it’s going to shake up the labor movement and flip the orthodoxy on its head,” said Justine Medina, a box packer and union organizer at JFK8 who had waited with an exuberant crowd in Brooklyn to hear the vote results.

The future of American unionizing efforts “can’t be about people coming in from the outside with an organizing plan that people have to follow,” said Sara Nelson, head of the flight attendants’ union, in an interview. “It has to come from within the workplace.”

Now, both the nascent JFK8 union and Amazon face pressing questions. The union, with no traditional infrastructure, experience or leadership, is likely to face a legal battle over the vote and challenging contract negotiations. The company, which did not respond to a request for comment for this article, will have to decide whether to reconsider some of its tactics and address the underlying labor dissatisfaction that handed it such a sweeping defeat.

“Amazon wanted to make me the face of the whole unionizing efforts against them,” Mr. Smalls wrote in a tweet on Friday, appearing undaunted by the task ahead. “Welp there you go!”

The Walkout

When Amazon opened the sprawling JFK8 site in 2018, the company was both drawn to and wary of New York, America’s most important consumer market. The established Retail, Wholesale and Department Store Union announced a bold goal: to turn JFK8 into the first organized Amazon warehouse in the country.

Soon Amazon withdrew from its highly touted plan to open a second headquarters in the city, as a backlash grew over public subsidies it would receive and its history of opposing unions. But the talk of organizing JFK8 went nowhere. In labor circles, many believed that Amazon’s turnover was too high, and its tactics too combative, for a union to succeed.

When the first coronavirus cases were confirmed at JFK8 in March 2020, Mr. Palmer and Mr. Smalls confronted managers with safety concerns. Employees were increasingly worried about rising infection rates and felt that Amazon was not notifying them about cases in a timely manner, managers documented in newly released court records.

But Amazon refused to pause operations, saying it had taken “extreme measures” to keep workers safe. The pandemic had turned JFK8 into a lifeline for the city, where 24/7 shifts and a fleet of trucks delivered supplies as it went into lockdown.

As Amazon moved to fire Mr. Smalls that March, two human resource employees at JFK8 doubted the wisdom of his dismissal. “Come on,” one messaged. Mr. Smalls was outside, peaceful and social-distancing, she wrote. His firing, she predicted, would be “perceived as retaliation.” But the termination proceeded.

After the firing, the chief counsel’s smear against Mr. Smalls — a full apology came only later — and the dismissal of another protester, the two friends resolved to take action. Mr. Smalls was outspoken, Mr. Palmer deliberate. They were both Black men from New Jersey and the same age (31 then, 33 now). Both had dropped out of community college, prided themselves on high scores on Amazon’s performance metrics and once hoped to rise within the company.

Now they made new plans. Mr. Palmer would keep working at JFK8, the better to change it from inside.

In early 2021, they took a road trip to another Amazon warehouse. When workers held a union drive in Bessemer, Ala., Mr. Palmer and Mr. Smalls wanted to witness it. But they found organizers from the retail union — the one that had previously declared an interest in JFK8 — less than welcoming to them and thought the professionals seemed like outsiders who had descended on the community.

By April, workers in Bessemer had rejected the union by more than a 2-to-1 margin. Mr. Palmer and Mr. Smalls declared their intention to organize JFK8, but few took them seriously. Why should they win when better-funded, more experienced operatives had been beaten?

Turnover and Morale

As they set about their first task — gathering thousands of worker signatures to trigger a unionization vote — cracks in Amazon’s employment model were plainly evident.

JFK8 had offered jobs to workers laid off by other industries during the pandemic. But a New York Times investigation last June revealed that the warehouse was burning through employees, firing others because of communication and technology errors and mistakenly depriving workers of benefits.

Black associates at JFK8 were almost 50 percent more likely to be fired than their white peers, according to an internal document. Even before the pandemic upended work, Amazon warehouses had an astonishing turnover rate of 150 percent.

As Mr. Palmer and Mr. Smalls approached workers at the bus stop, Amazon’s tone toward its employees kept shifting. Jeff Bezos, the company’s founder, was handing over the role of chief executive to Andy Jassy, and the company raised wages and added the goal of being “Earth’s best employer” to its guiding principles. It pledged to listen to complaints and improve working conditions.

At other times, it was contentious. In a widely publicized Twitter exchange about the Bessemer organizing, Amazon sounded so dismissive about workers who could not take bathroom breaks and had to urinate in bottles that it had to apologize.

In May at JFK8, an anti-union consultant called the mostly Black labor organizers “thugs,” according to a complaint filed against Amazon by the N.L.R.B. The retailer denied the episode.

And in November, the labor agency said Amazon had showed “flagrant disregard” for the law and threw out the results of the Bessemer warehouse vote, ordering another.

That fall, after months of gathering support, the New York union organizers delivered more than 2,000 signatures to the labor board, but they were rejected for not meeting the minimum required to hold an election. Mr. Smalls said Amazon had submitted payroll data to the board indicating that the company believed half the people who had signed cards no longer worked at the warehouse.

“After all those months of hard work, it seemed like the momentum was gone,” Mr. Palmer recalled in an interview. Between working his shifts and organizing at JFK8 on his time off, he had spent barely a day away from the warehouse for months. Some of the employees he approached were skeptical of unions or dues, or just grateful for Amazon’s health care and pay, which starts above $18 an hour at JFK8. Others seemed too exhausted and wary to even engage.

The Path to Victory

To press onward, the union leaders posted the TikTok videos, made outdoor s’mores and sang along to hip-hop and Marvin Gaye. When workers faced family crises, the budding union prayed. One fired employee became homeless, and the group set up a fund-raising campaign.

Their near-constant presence at the warehouse helped. “The more comfortable they get with us, that’s when they start opening up to us,” Mr. Palmer said of other workers.

Some union sympathizers took jobs at JFK8 specifically to help the organizing effort, according to Ms. Medina, who was among them.

Amazon countered with the full force of its anti-union apparatus. It monitored organizers’ social media, court filings show, pelted workers with text messages and blanketed the warehouse with signs saying “Vote NO” or claiming the union leaders were outsiders. The company often held more than 20 mandatory meetings with workers a day, The Times reported last month, in which managers and consultants cast doubt on the effort.

“The Amazon Labor Union has never negotiated a contract,” one presentation said. Dues would be expensive, it continued, and the union “has no experience managing this massive amount of money.”

Andro Perez, 35, works at a smaller Amazon warehouse near JFK8, where another union vote is scheduled this month. He’s leaning toward voting yes, he said, because Amazon’s mandatory meetings mostly criticized unions. He would rather his employer address the question: “What could you do better?”

The organizers at JFK8 fought back, filing dozens of complaints with the N.L.R.B. claiming that Amazon violated workers’ rights to organize. Amazon has denied their allegations, but the labor board found many to be credible and pursued them in administrative court.

By Christmas, the organizers scored a major legal win. Amazon agreed to a nationwide settlement, among the largest in the agency’s history, that said workers could stay in the buildings to organize when they were off the clock.

With that, the organizers moved their potlucks indoors, giving them more access and legitimacy. Mr. Smalls’s aunt provided home-cooked soul food: macaroni and cheese, candied yams, collard greens and baked chicken.

“What you do is you create a community that Amazon never really had for workers,” said Seth Goldstein, a lawyer who represented the organizers free of charge.

One day this February, Mr. Smalls was bringing lunch to the break room when Amazon called the police, saying he had trespassed. He and two current employees were arrested. The response may have backfired: The union’s videos of the episode on TikTok have been viewed hundreds of thousands of times.

Kathleen Lejuez, 41, employed by Amazon for nine years, said she was not a “union fan” but voted for the organizing effort to send a message to a company that she felt had lost its connection to workers. “The humanity at Amazon is gone,” she said in an interview.

In the weeks before the count, Amazon, which has consistently said its workers are best served by a direct relationship with the company, laid the groundwork for potential challenges to the election — arguing in legal filings that the labor board had abandoned “the neutrality of their office” in favor of the union.

On Friday morning inside the agency’s offices in Brooklyn, Mr. Smalls, in siren-red streetwear, sat next to Amazon’s lawyer to review each ballot. His knee jittered as each vote was presented.

The votes were tallied — 2,654 for the union, 2,131 against. With a comfortable margin secured, Mr. Palmer, Mr. Smalls and other representatives emerged into the spring light, screamed with joy and clasped one another in a tight circle.

A few miles away, at JFK8, workers were stealthily monitoring the results in between packing and stowing boxes. There was no formal announcement. Instead, a shout rose up from somewhere on the floor: “We did it! We won!”

Grace Ashford and Noam Scheiber contributed reporting.