DETROIT – The United Auto Workers union is threatening to go on strike against Fiat Chrysler after its membership rejected a tentative contract deal with the company.

In a statement, Fiat Chrysler said Tuesday that it received a strike notice from the union, and that it continues to work toward reaching an agreement.

A letter to Fiat Chrysler that was posted on the UAW website Tuesday says the union is ending its contract with FCA at 11:59 p.m. Wednesday.

Union members overwhelmingly rejected a tentative agreement with the company last week, with members calling for an end to a two-tier pay structure, more specific guarantees of new vehicles for U.S. factories and a return of cost-of-living pay raises that the union gave up to help the company in bad times. Now that Fiat Chrysler is making healthy profits, members want a bigger slice.

Sixty-five percent of FCA’s 40,000 union workers voted against the four-year deal. UAW President Dennis Williams said after the rejection that he would return to the bargaining table with Fiat Chrysler in an effort to get a deal that would be ratified.

Kristen Dziczek, director of the labor and manufacturing group at the Center for Automotive Research, an industry think tank, said the contract termination notice sounds to her like the membership’s demands weren’t received well at Fiat Chrysler’s headquarters.