Talks for a new four-year labor contract between General Motors and its striking workers took a “turn for the worse” on Sunday after the United Auto Workers rejected the largest US automaker’s latest offer, but the two sides were still talking.

GM made an offer to the union that basically repeated one the UAW had previously rejected, Terry Dittes, the UAW vice president in charge of the GM department, said in a letter to members. The union provided a copy of the letter to Reuters.

“These negotiations have taken a turn for the worse,” he said.

“We, in this union, could not be more disappointed with General Motors,” Dittes said. “The company has shown an unwillingness to fairly compensate … the UAW.”