At a sprawling Whole Foods Market in Philadelphia, a battle is brewing. The roughly 300 workers are set to vote on Monday on whether to form the first union in Amazon’s grocery business.

Several store employees said they hoped a union could negotiate higher starting wages, above the current rate of $16 an hour. They’re also aiming to secure health insurance for part-time workers and protections against at-will firing.

There is a broader goal, too: to inspire a wave of organizing across the grocery chain, adding to union drives among warehouse workers and delivery drivers that Amazon is already combating.

“If all the different sectors that make it work can demand a little bit more, have more control, have more of a voice in the workplace — that could be a start of chipping away at the power that Amazon has, or at least putting it in check,” said Ed Dupree, an employee in the produce department. Mr. Dupree has worked at Whole Foods since 2016 and previously worked at an Amazon warehouse.

Management sees things differently. “A union is not needed at Whole Foods Market,” the company said in a statement, adding that it recognized employees’ right to “make an informed decision.”

Workers said that since they went public with their union drive last fall, store managers had ramped up their monitoring of employees, hung up posters with anti-union messaging in break rooms and held meetings that cast unions in a negative light.

Audrey Ta, who fulfills online orders at the store, said that she planned to vote in favor of unionizing with the United Food and Commercial Workers, but that there was unease among the workers. She has stopped wearing her union pin on the job.

“People keep their head down and try to talk not to talk about it,” Ms. Ta said. “Management really pays attention to what we talk about.”

Whole Foods said it had complied with all legal requirements when communicating with employees about unions.

U.F.C.W. Local 1776, which represents workers in Pennsylvania, has filed unfair labor practice charges with the National Labor Relations Board, accusing Whole Foods of firing an employee in retaliation for supporting the union drive. The union also accused the chain of excluding the store’s employees from a pay raise that had been given this month to all its other workers in the Philadelphia area.

“They’re treating them differently,” said Wendell Young IV, president of U.F.C.W. Local 1776. “They’re discriminating against them for trying to form a union.”

Whole Foods denied allegations of retaliation. The company argued that it cannot legally change wages during the election process, and that it had delayed a raise until after the election to avoid the appearance of trying to influence votes.

A majority of the store’s workers signed union authorization cards last year before the union filed a petition for an election. But Ben Lovett, an employee who has led the organizing, said he expected the election to be close.

Whole Foods is the latest segment of Amazon’s business to confront the prospect of a union. In 2022, workers on Staten Island voted to form Amazon’s first union in the United States; it is now affiliated with the International Brotherhood of Teamsters. Amazon disputed the election outcome and has refused to recognize or bargain with the union pending a court challenge.

Delivery drivers, who work for third-party package delivery companies serving Amazon from California to New York, have also mounted campaigns with the Teamsters.

Rob Jennings, an employee in the prepared foods section of the Philadelphia store, has worked there for nearly two decades. He said he noticed a series of changes after Amazon bought the chain in 2017: a program that offered employees a portion of the store’s budget surplus was scrapped, part-time workers lost health insurance, staffing levels started to decline.

Even though Whole Foods had never been a worker paradise, Mr. Jennings said, “I have a fantasy about bringing back all the things they took away.”

Whole Foods said in a statement that the abandoned profit-sharing program did not evenly benefit all employees and that the company invested in wages instead; that part-time workers lost the ability to buy health insurance through the company and did not lose funded health insurance; that part-time workers receive other benefits like in-store discounts and a 401(k) plan; and that the company is committed to keeping stores appropriately staffed.

Khy Adams first knew the Philadelphia store as a high school hangout. She had been wanting to work there for years when, in August, she landed a job overseeing the hot foods bar.

But she did not find the work-life balance she had sought, she said, with management expecting an unreasonable level of availability. She said she hoped a union could help improve conditions.

In addition to Amazon’s pushback, the political transformation in Washington may pose hurdles. After the Biden administration’s embrace of unions, President Trump is expected to appoint a new N.L.R.B. general counsel whose approach could make it harder for organizing campaigns to succeed.

“Amazon has the machine behind them to prolong this, to shut this down, to make it the hardest thing for us to continue to work toward,” Ms. Adams said of the campaign to unionize.