Seven Amazon fulfillment facilities across the U.S. were targeted by strikes by workers who deliver packages from them, according to the International Brotherhood of Teamsters, the union that represents them.

The Teamsters said it would launch the largest strike against Amazon in U.S. history beginning at 6 a.m. EST on December 19, specifically mentioning Amazon facilities DBK4 in New York City; DGT8 in Atlanta; DFX4, DAX5, and DAX8 in Southern California; DCK6 in San Francisco; and DIL7 in Skokie, Ill. The New York Times reported thousands of delivery workers at the seven facilities had walked out that morning. 

The statement from the Teamsters said: “The nationwide action follows Amazon’s repeated refusal to follow the law and bargain with the thousands of Amazon workers who organized with the Teamsters.”

“If your package is delayed during the holidays, you can blame Amazon’s insatiable greed. We gave Amazon a clear deadline to come to the table and do right by our members. They ignored it,” said Teamsters general president Sean M. O’Brien. 

According to the Times, Amazon said it expected the seven distribution centers to operate normally.

Amazon claims it has no obligation to bargain with the workers, because they are employees of companies that Amazon uses to deliver packages to customers, and therefore not its employees. But the union and the workers argue that Amazon ultimately controls their working conditions.

The National Labor Relations Board has investigated several cases of Amazon refusing to bargain with workers that serve its supply chain, and has issued at least one complaint finding the workers to be Amazon employees, concluding the company is breaking the law by failing to bargain with them. 

In response, Amazon joined SpaceX in directing attorneys for the two companies to lodge a motion with a panel of judges at the Fifth Circuit Court of Appeals that the labor agency, created by Congress in 1935, is unconstitutional, according to National Public Radio.