Thousands of delivery drivers who work for Amazon third-party contractors are now on strike, The New York Times reports. The workers are striking after “Amazon’s repeated refusal to follow the law and bargain with the thousands of Amazon workers who organized with the Teamsters,” according to a Teamsters press release.

Workers are picketing at Amazon warehouses from Atlanta, New York City, San Francisco, Southern California, and Skokie, Ill., with other Amazon Teamsters “prepared to join them,” the Teamsters say. “Teamsters local unions are also putting up primary picket lines at hundreds of Amazon Fulfillment Centers nationwide.”

The National Labor Relations Board issued a complaint against Amazon earlier this year, saying that Amazon and one of its third-party contractors are joint employers of delivery drivers and that it has “a legal duty to recognize and bargain with the Teamsters Union,” per another Teamsters press release.

Amazon spokesperson Kelly Nantel shared the following statement with New York City’s WPIX and with The Verge:

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. The truth is that the Teamsters have actively threatened, intimidated, and attempted to coerce Amazon employees and third-party drivers to join them, which is illegal and is the subject of multiple pending unfair labor practice charges against the union.

Amazon employees who have organized with the Teamsters voted last week to authorize a strike.

Update, December 19th: Added that Amazon sent us a statement.