DETROIT — The United Auto Workers has filed unfair labor practice charges with the National Labor Relations Board against Honda Motor, Hyundai Motor and Volkswagen, accusing the automakers of unlawfully interfering with worker organizing, the union said Monday.

UAW alleges management at three facilities — for Honda in Greensburg, Indiana; Hyundai in Montgomery, Alabama; and Volkswagen in Chattanooga, Tennessee — have participated in illegal “union-busting as workers organize to join the UAW.”

The union alleges the activities range from surveillance of workers at Honda to confiscating, destroying, and prohibiting “pro-union materials in non-work areas during non-work times” at Hyundai.

At VW, the UAW alleges management has “harassed and threatened workers for talking about the union; confiscated and destroyed pro-union materials in the break room; attempted to intimidate and illegally silence pro-union workers; and has attempted to illegally prohibit workers from distributing union literature and discussing union issues in non-work areas on non-work time.”

“These companies are breaking the law in an attempt to get autoworkers to sit down and shut up instead of fighting for their fair share,” UAW President Shawn Fain said in a statement. “But these workers are showing management that they won’t be intimidated out of their right to speak up and organize for a better life.”

Volkswagen told CNBC it “respects our workers’ right to determine who should represent their interests in the workplace” and it takes “claims like this very seriously and will investigate accordingly.”

Spokespeople for Honda and Hyundai did not immediately respond to requests for comment. 

The filings were not immediately available on the NLRB’s website, but the union provided them to CNBC.

The actions that prompted the allegations against the employers occurred during the last six months, according to the filings, which were signed by UAW outside counsel Benjamin Dictor, an attorney with New York-based Eisner Dictor & Lamadrid.

The charges come roughly two weeks after the UAW said it was launching an unprecedented campaign to organize 13 nonunion automakers in the U.S. after it secured record contracts with the three Detroit automakers — General Motors, Ford Motor and Stellantis.

UAW membership has been nearly cut in half since 2001, from about 700,000 that year to 383,000 at the beginning of 2023. It peaked at 1.5 million in 1979.

Fain has vowed to move beyond the “Big Three” and expand to the “Big Five or Big Six” by the time its four-and-a-half-year contracts with the Detroit automakers expire in April 2028.