The International Brotherhood of Teamsters said workers at seven Amazon facilities will begin a strike on Thursday morning, an effort by the union to pressure the e-commerce company for a labor agreement during a key shopping period.

The Teamsters say the workers, who authorized strikes in the past few days, are joining the picket line after Amazon ignored a Dec. 15 deadline the union set for contract negotiations. Amazon says it doesn’t expect an impact on its operations during what the union calls the largest strike against the company in U.S. history.

The Teamsters say they represent nearly 10,000 workers at 10 Amazon facilities, a small portion of the 1.5 million people Amazon employs in its warehouses and corporate offices.

At one warehouse, located in New York City’s Staten Island borough, thousands of workers who voted for the Amazon Labor Union in 2022 and have since affiliated with the Teamsters. At the other facilities, employees - including many delivery drivers - have unionized with them by demonstrating majority support but without holding government-administered elections.

The strikes happening Thursday are taking place at one Amazon warehouse in San Francisco, California, and six delivery stations in southern California, New York City; Atlanta, Georgia, and Skokie, Illinois, according to the union’s announcement. Amazon workers at the other facilities are “prepared to join,” the union said.

“Amazon is pushing its workers closer to the picket line by failing to show them the respect they have earned,” Teamsters General President Sean M. O’Brien said in a statement.

The Seattle-based online retailer has been seeking to re-do the election that led to the union victory at the warehouse on Staten Island, which the Teamsters now represent. In the process, the company has filed a lawsuit challenging the constitutionality of the National Labor Relations Board.

Meanwhile, Amazon says the delivery drivers, which the Teamsters have organized for more than a year, are not its employees. Under its business model, the drivers work for third-party business, called Delivery Service Partners, who drop off millions of packages to customers everyday.

“For more than a year now, the Teamsters have continued to intentionally mislead the public – claiming that they represent ‘thousands of Amazon employees and drivers’. They don’t, and this is another attempt to push a false narrative,” Amazon spokesperson Kelly Nantel said in a statement.

The Teamsters have argued Amazon essentially controls everything the drivers do and should be classified as an employer. Some U.S. labor regulators have sided with the union in filings made before the NLRB. In September, Amazon boosted pay for the drivers amid the growing pressure.