The union that represents workers at Southern California’s three major supermarket chains on Friday strongly criticized the grocers’ first comprehensive contract offer, calling it “unacceptable” and making its first veiled threat of a possible work stoppage.

Representatives of Vons, Ralphs and Albertsons have been in talks with the United Food and Commercial Workers since early March, and union leaders say the chains had not made any offers on wages and benefits, the key issues,

But after three days of talks ended Friday, May 24, the websites of UFCW’s seven locals said the grocers’ first offer of wage and benefits changes were “unacceptable.” The union represents about 60,000 workers spread out over all of Southern California.

According to the union postings, the offer would provide pay increases of just 1%.

Greg Conger, president of Local 324, which represents workers in Orange County, said the stores have proposed that cashiers — the best-paid clerks in the stores — be formally downgraded to positions with lower pay scales.

Conger said in an interview that the chains have proposed fewer payments into the union trust account that funds health care coverage. While this would not immediately affect medical coverage, it would likely reduce the levels of health care in the future. The web posting also said the grocery chains have refused to submit a plan to adequately fund pensions.

“We’ll try to figure out what our next step will be, but they are not bargaining in good faith,” Conger said.

Representatives of the three chains did not reply to requests for comment.

Conger said that more talks will be held in two weeks, and if UFCW doesn’t see progress, then leaders will go to its members to discuss authorizing a strike. This is used by unions to increase negotiation leverage and does not necessarily mean a work stoppage is imminent.

In 2003 and 2004, a four-month strike at Albertsons, Vons and Ralphs shook up Southern California’s grocery industry and cost the stores billions of dollars. Since then contract talks have frequently been contentious, and strikes have been authorized but not carried out.

Last month, UFCW workers walked off their jobs at the New England chain Stop & Shop. The 11-day strike ended April 21.