GM is being sued by the UAW for using temporary workers at the plant instead of laid-off employees.

If there wasn’t tension between the UAW and General Motors due to the company’s restructuring plans to close five plants, the new lawsuit filed by the union over the use of temporary workers should ensure there is now.

The United Auto Workers said on Thursday it was suing GM about labor contract violations due to the alleged use of temporary workers at an Indiana assembly plant.

The lawsuit was filed on Wednesday in U.S. District Court in Ohio. At the heart of the matter, according to the union, is the fact that GM used temporary workers at the plant when there are 1,000 laid-off hourly employees with rights to transfer to plants with openings — specifically the Fort Wayne, Indiana plant.

“UAW members negotiated a binding agreement and we expect General Motors to follow the contract they agreed to and GM members ratified,” UAW Vice President Terry Dittes said in a statement.

(Unifor puts pressure on GM in new advertising campaign. Click Here for the story.)

GM began the process to bring about 50 workers from the Lordstown, Ohio plant – one of the five slated to be closed by GM in its reorganizations – to Indiana late last year. It added that is has been engaged in ongoing talks with the union regarding staffing needs in Fort Wayne. It declined to comment directly on the lawsuit, however.

A UAW lawsuit said as many as 700 Lordstown workers could be used at an Indiana plant instead of temporary workers.

The union notes that of the 1,000 laid-off employees eligible to take the jobs currently held by temps, 700 of those are from the Lordstown facility.

The union said in the lawsuit that on May 31, 2018, it approved GM’s request to use temporary workers at the Indiana plant through the end of August 2018, Reuters reported, to support the launch of new full-size pickup trucks.

(Click Here for more about Senators pressuring GM to halt $14B stock buyback plan.)

At the end, GM wanted to extend the period it could use the temporary workers. The UAW agreed, but pushed for the idled workers to be hired to fill the openings, according to the lawsuit. In the end, the UAW denied GM permission to use the temporary workers beyond the end of November.

The UAW said many of the 690 Lordstown workers on layoff had applied to transfer to the openings at Fort Wayne, Reuters reported, adding that the UAW is asking the court to make affected workers whole through back wages lost, benefits, relocation costs and seniority credit.

The suit signals the UAW’s intention to play hardball with General Motors going forward, and with a new national contract needing to be negotiation this summer, the automaker could be in for a tough set of talks.

(To see more about Mary Barra’s radical reshaping of General Motors, Click Here.)

Complicating these talks is the pressure the company is also getting from Canadian hourly workers, whose union, Unifor, just released an advertising campaign pressuring GM to reopen the plant in Oshawa, Ontario,