Negotiators for the United Auto Workers and General Motors Corp. resumed concession talks Sunday after the union walked out of a meeting on Friday night in a dispute over payments to a union-administered retiree health-care fund.

The talks are still focusing on exchanging the company's cash payments into the health care trust for GM stock, according to a person briefed on the talks who didn't want to be identified because the bargaining is private.

GM and UAW officials declined comment.

The talks come at a critical time as GM races against a Tuesday deadline to submit a plan to the U.S. government showing how it can become viable.

The Detroit-based auto giant is living on $9.4 billion US in government loans, and the Treasury Department must approve its viability plan for the company to get $4 billion more. Chrysler LLC, which has received $4 billion in government loans and wants an additional $3 billion, faces the same deadline.

At GM, UAW negotiators walked away because the company made demands that were "detrimental to retirees and the ability to provide health care," according to a person, who asked not to be identified.

Under terms of the loans to GM and Chrysler laid down by the administration of former U.S. president George W. Bush, both companies must gain concessions from unions and debt holders. Among targets for concessions is GM's cash contribution to a trust fund that will take over the obligation for retiree health care starting next year.

GM says it owes $20.4 billion to the fund, and the loan terms set a target of giving the union half of the value in cash and half in GM stock. The trust fund would take over health-care payments for GM's roughly 500,000 blue-collar retirees and spouses starting Jan. 1, 2010.

The trust, called a voluntary employees beneficiary association, would let GM move about $46.7 billion in retiree health-care costs from its books, making it more cost-competitive with Asian automakers. It is the key feature of a four-year contract signed in 2007 with the UAW.

The union has said that if fully funded, the trust would provide health care to retirees for 80 years.