Union leaders representing 30,000 grocery workers in the Puget Sound area are threatening a strike. On Wednesday workers staged pickets outside 38 supermarkets.
The key sticking point in negotiations with Safeway, QFC, Fred Meyer and Albertsons is health care.
Both sides say grocery workers have good health benefits now.
The dispute is over future eligibility.
Workers can now get individual health care if they work 16 hours per week and family coverage if they work 20 hours per week.
The grocery companies want to raise the threshold for health coverage to 30 hours per week, in line with what nonunion competitors will be required to pay under the Affordable Care Act.
"We don't want to be in a position where we're stuck covering part-time employees and our competitors don't have to cover them," said Scott Powers of Allied Employers, which represents the grocery companies.
Workers say anyone losing health coverage would seriously suffer.
"It will be terrible, a lot of people are working just to get their health benefits," said Safeway worker Ariana Davis.
Contract talks began in March and more negotiation sessions are scheduled. The union has scheduled votes for late September, but doesn't know yet if those will be votes on contract proposals or strike authorization.
A grocery strike was averted around Thanksgiving 2010 by a last-minute contract agreement.