After Amazon employees at a massive warehouse on Staten Island scored an upset union victory last month, it turned the union's leaders into celebrities, sent shock waves through the broader labor movement and prompted politicians around the country to rally behind Amazon workers. It appears that it has created problems within Amazon's management ranks.

Four current and former employees with knowledge of the situation who spoke on the condition of anonymity said that on Thursday, Amazon informed more than half a dozen senior managers that they were being fired.

The firings, which occurred outside of the company's typical employee review cycle, were seen by the managers and other people who work at the facility as a response to the victory by the Amazon Labor Union, three of the people said. In one of the biggest victories for organized labor in a long time, workers at the warehouse voted by a wide margin to form the first union at the company in the United States.

The news of the shake-up spread through the warehouse. The company's response to the unionization effort was implemented by many of the managers. Several were veterans of the company with more than six years of experience.

Workers who supported the union complained that the company's health and safety protocols were too easy to follow and that the company pushed them too hard to meet performance targets. The pay at the warehouse is too low to live on in New York City.

An Amazon spokeswoman said the company made the management changes after it had spent several weeks evaluating aspects of the warehouse.

Two people said that the managers were told they were being fired. Some of the managers have recently received positive reviews, according to one of the people.

The Staten Island facility is Amazon's only fulfillment center in New York City and for a year current and former workers organized to form an upstart, independent union.

The National Labor Relations Board was biased in favor of the union and the company is challenging the election. The union is trying to keep up the pressure on Amazon so it can negotiate a contract.

The president of the Amazon Labor Union testified before a Senate committee about whether companies that violate labor laws should be denied federal contracts. Mr. Smalls went to a White House meeting with other labor organizers and asked President Biden to pressure Amazon to recognize his union.

A White House spokeswoman said that it was up to the National Labor Relations Board to certify the results of the recent election, but affirmed that Mr. Biden had long supported collective bargaining and workers' rights to unionize.

Amazon has said that it provides pay above the minimum wage with solid benefits like health care for full-time workers as soon as they join the company, and that it invested $300 million on safety projects in 2021.

In the run-up to the election, company officials and consultants held more than 20 mandatory meetings per day with employees to convince them not to support the union. The officials highlighted the amount of money the union would collect from them and emphasized the uncertainty of collective bargaining, which they said could leave workers worse off.

Labor experts say that such claims can be misleading because it is very rare for workers to see their compensation fall as a result of the union bargaining process.

This is not a finished story. You can check back for updates.

Sheelagh McNeill and Grace Ashford contributed to the research.