The National Labor Relations Board has filed a complaint against Volkswagen because the company hasn't bargained with the United Auto Workers union.

The complaint comes after 71 percent of maintenance employees at the plant voted in favor of representation by the UAW in December 2015.

The complaint isn't a new unfair labor practice complaint, but rather a follow-up to an original UAW charge filed in January. 

The complaint mentions increases in health insurance costs and changes in work hours for employees—subjects that are matters of collective bargaining, according to the NLRB. It also says that VW must file and answer to the complaint by May 24.  

Volkswagen's position has been that all employees—not only maintenance workers—should be able to decide whether they want union representation. 

"This is why we fundamentally disagree with the decision to separate Volkswagen maintenance and production workers and will continue our effort to allow everyone to vote as one group on the matter of union representation," spokesman Scott Wilson said via email. "Thus, we are continuing our efforts to have the unit reviewed by the U.S. Court of Appeals. Until the court makes a decision on this matter, we are unable to bargain with the UAW."

But the UAW has continued to put pressure on VW to bargain.

For example, local UAW members recently spoke in a video about their dissatisfaction with working conditions.

Members also recently had a news conference at Volkswagen's annual general meeting, calling for VW to recognize UAW's local chapter. 

"With its behavior, Volkswagen violates its own principles of social responsibility, as well as the global framework agreement with the worldwide trade union IndustriALL," Steve Cochran, president of UAW’s Chattanooga chapter Local 42, said, according to a prepared statement. "UAW, therefore, calls on the company’s management to recognize UAW Local 42 as the representative of VW employees in Chattanooga and to enter into bargaining negotiations with them."

Local attorney Dan Gilmore, who has expertise in labor law and has been following the VW–UAW situation, said that the language in the latest complaint could imply that changes in health care and hours were directed at members who support the union. 

"In other words, VW is retaliating against the unit employees because of how a majority of them voted," he said via email.    

On the other hand, Gilmore said the union would likely have a hard time showing that premium increases or schedule changes were made in retaliation because the changes likely affect all employees, not just the smaller bargaining unit. 

He also pointed out that the NLRB has already said that VW has a duty to bargain with the union, despite the fact that the decision is under appeal. 

"The continuing irony ... is that VW, unlike most any other employer in the U.S. in its position, still has no animosity toward those employees who voted for the union in either election," he also said. "It simply wants ALL of them to have another chance to vote. That is the only way VW can say that it allowed its employees to decide their own future, which continues to be their public position."