CHATTANOOGA (AP) — Four workers at Volkswagen's plant in Chattanooga have filed complaints with the National Labor Relations Board saying the company is coercing employees into approving the United Auto Workers as their bargaining agent.

Volkswagen's top labor official, Bernd Osterloh says that Chattanooga would need to organize in order to compete for a new SUV that VW hopes to build in the U.S., requiring 800 new workers.

Matt Patterson leads the anti-union Center for Worker Freedom at the Americans for Tax Reform. Patterson told WPLN-FM in Nashville that comment sounds like a threat to him.

UAW Regional Director Gary Casteel told the Chattanooga Times Free Press the cards signed by the workers clearly state the workers are supporting the UAW's effort to represent them.

"It's as binding and legal as any vote," he said.

For three of the four workers who signed onto this complaint, it's their second grievance filed with the NLRB. The first alleged that the UAW bribed employees to sign their union cards. However, the union cards specifically say that anyone is welcome to revoke them at any time.

In the charge, the workers said VW's alleged threat "interfere(s) with Chattanooga facility employees' rights to choose whether or not to engage in self-organization to form, join, or assist labor organizations."

Mark Mix, president of the foundation that has attorneys working with the workers, said in a statement that with reports that VW is considering Chattanooga to build its new sport utility vehicle, "this is no idle threat."

"If VW management was discouraging workers from joining the UAW with threats, there's little question that an NLRB prosecution would have already begun at the UAW's behest," Mix said.

A VW plant spokesman said Wednesday the company had no comment on the NLRB filing.

"We know how important that (second) vehicle is for Chattanooga," said Bernd Osterloh, head of VW's global works council, in Germany.

Eight VW workers had earlier filed NLRB charges against the UAW, alleging coercion and intimidation related to authorization cards the union is asking employees for the automaker to sign.

The UAW has denied those charges.

VW and the UAW are talking about the setup of a works council in Chattanooga. The UAW has said that VW accepting the cards would be the least divisive way to handle the situation rather than hold a secret-ballot vote.