United Auto Workers (UAW) union members at General Motors have set a Monday afternoon deadline for reaching a deal on cost cutting and competitiveness.
Employees are working at GM without a new contract
The carmaker wants staff to give up some of their expensive benefits such as pensions and health insurance.
In return the union wants GM to commit to maintaining production in the US.
If no agreement is reached, and the union receives to assurances on job security, it has threatened that 73,000 GM factory workers will go on strike.
"We're shocked and disappointed that General Motors has failed to recognize and appreciate what our membership has contributed during the past four years," said UAW President Ron Gettelfinger in a statement.
GM's 73,000 UAW employees saw their contracts expire on Friday, 14 September.
The talks are important because the UAW's contracts with Ford and Chrysler will be based on the GM agreement.
The three Detroit-based carmakers are trying to cut costs as they attempt to recover from combined losses of $15bn (£7.5bn) last year.
GM, Ford and Chrysler say that their workers, on average, cost them more than $30 an hour more than Toyota's.
"We are fully committed to working with the UAW to develop solutions together," GM spokesman Dan Flores said. "We will continue focusing our efforts to reach an agreement as soon as possible."
The talks deadline has been set at 11am local time (1500 GMT).