SEATTLE – About 21,000 Puget Sound-area grocery workers are edging closer to a strike.

Union leaders are warning that workers could walk off the job Monday evening at four grocery chains if no contract agreement is reached.

Organizers gathered Saturday night to launch a food donation drive to support the striking workers.

United Food and Commercial Workers spokesman Tom Geiger said a 72-hour strike notice was given Friday night to QFC, Safeway, Albertsons and Fred Meyer stores. The union erected a giant strike countdown “clock” at Westlake Park in downtown Seattle.

Unresolved issues include wages, holiday pay and “even cuts to (workers’) cherished health care plans,” the spokesman said, adding the two sides have been in talks for more than six months.

Union members in King, Snohomish, Pierce, Kitsap, Thurston and Mason counties have rejected current proposals and voted to authorize a strike.

The last area grocery strike was in 1989 and lasted nearly three months.