DENVER -- Thousands of unionized grocery workers at Safeway voted Saturday night to give their union the authority to call on workers to strike as early as Monday.

The decision doesn't necessarily mean that workers will strike. A union spokesperson said that workers will be going to work for the foreseeable future.

Contracts were expiring Saturday night for about 17,000 King Soopers, Safeway and Albertsons workers represented by United Food and Commercial Workers Local 7 in Colorado. The union said all three chains have offered similar proposals, but the sides still disagree over wages and pension benefits.

King Soopers and Safeway have agreed that one chain can lock out its employees if workers at the other chain go on strike. The two chains also have accepted applications for temporary workers, if employees walk out.

Safeway workers were expected at work Sunday, but in a statement the union said workers could begin striking Monday if the company does not respond with a "new proposal and an offer to return to the bargaining table." Results of the vote were not immediately released.

Safeway spokeswoman Kristine Staaf said the company has been notified of the vote and has told the union the company is willing to renew bargaining.

"We hope that Safeway will come back to the bargaining table," said Crisanta Duran, associate legal counsel for UFCW Local 7.

King Soopers, meanwhile, proposed extending its contract until May 30, which the union accepted despite misgivings about provisions that allow for a worker lockout.

All parties say they hope to reach contracts without a strike.

King Soopers and Safeway have offered similar five-year contracts with raises of 10 cents an hour for courtesy clerks and 25 cents per hour for journeymen, but most workers' wages would be frozen, Duran said.

The companies have said they offered to contribute millions of dollars more to workers' pension fund, but Duran said overall pension benefits would still fall.

Thirty-two-year Safeway employee Kim Pleasant, a checker, said there also has been no progress on changing a two-tier system that offers fewer health and pension benefits to workers who joined the company after 2005.

Pleasant, 52, voted Saturday to strike. "There's no way in heck I'm going to take what they just gave me," said Pleasant, whose husband is unable to work.

Workers wearing black shirts that said "United we bargain" in yellow letters on one sleeve and "Divided we beg" on the other milled outside a Denver hotel room where Safeway employees voted Friday and Saturday.

The union says grocers are benefiting as more customers avoid restaurants and buy food to cook at home. The grocery chains contend they have to compete with low-cost, non-unionized competitors as health care costs rise and the economy wrecks pension plans.

Even without a strike, talks have been contentious, with the union filing complaints against all three grocers with the National Labor Relations Board. The board is reviewing the complaints, but that process could take weeks.

Gov. Bill Ritter on Friday urged the sides to redouble their efforts in contract talks, saying he was concerned about what a strike or lockout could do to grocery workers and shoppers.

Benita Collazo, a single mother of a teenager, said she would be upset if Safeway workers walk out and she gets locked out from her job as a checker at King Soopers, but she said workers at both chains would be in the same boat.

"It'd be a sad thing not to be able to work, have no income to pay the bills," she said.

In 1996, King Soopers workers voted to strike, prompting Safeway to lock out its workers.

The union is set to begin negotiating contracts Monday for Western Slope workers. Those contracts have historically been modeled by what happens in negotiations for Front Range workers.