The United Automobile Workers union on Monday accused three foreign automakers of unfair labor practices, claiming they interfered with workers’ efforts to build support for the union at U.S. factories.

The union said it had filed a complaint with the National Labor Relations Board, alleging that the automakers — Honda, Hyundai and Volkswagen — had tried to prevent employees from discussing UAW representation at work and that the companies were blocking those who had done had discriminated.

The action came two weeks after the UAW announced an effort to unionize non-union factories owned by 10 foreign companies, along with domestic manufacturers Tesla and Rivian, which make electric vehicles. The union has tried unsuccessfully in recent years to unionize some of these companies’ factories, but not on such a large scale at the same time.

The UAW said Monday that hundreds of workers at the Honda plant in Greensburg, Ind., and at the Hyundai plant in Montgomery, Alabama, and more than 1,000 workers at a Volkswagen plant in Chattanooga, Tenn., had signed cards expressing their expressed support for joining the union.

At Honda, the union said, workers “report being attacked and surveilled by management for pro-union activities,” while at Hyundai “management unlawfully placed pro-union materials in non-work areas during non-work hours during seized, destroyed and banned.”

It said Volkswagen had “harassed and threatened employees for talking about the union” and that it had “confiscated and destroyed pro-union materials in the canteen,” among other allegations.

In a statement, Volkswagen said it takes such allegations seriously and is investigating the matter. “Volkswagen respects the right of our employees to determine who should represent their interests in the workplace,” the company said. “We are committed to providing clear, transparent and timely information that helps inform our employees and managers of their legal rights and obligations.”

Honda and Hyundai did not immediately respond to requests for comment. When the UAW announced its organizing campaign last week, both automakers described their pay and benefit packages as beneficial and said union representation was not warranted.

Shawn Fain, the president of the UAW, lashed out at the three companies in the country a statement from the union. “These companies are breaking the law in an attempt to get auto workers to keep their mouths shut instead of fighting for their fair share,” he said. “But these workers are showing management that they will not be intimidated in their right to speak out and organize for a better life.”

The UAW is trying to organize foreign-owned factories after a six-week wave of strikes against three Detroit automakers — Ford, General Motors and Stellantis, which makes Jeep, Chrysler and other brands — resulted in contracts that delivered record wage increases and additional contracts . profit in benefits.

In addition to Honda, Hyundai and Volkswagen, the foreign companies the UAW said last week it was targeting are Toyota, Nissan, BMW, Mercedes-Benz, Subaru, Mazda and Volvo.