“What do you fight for? You fight for the dignity of working people,’’ Warren told an appreciative crowd. “Unions built America’s middle class — unions will be rebuilding American’s middle class.”

Warren greeted the workers on the sidewalk a short distance from the chain’s McGrath Highway store shortly after 11 a.m. She shook hands with some, posed for selfies with others, and then grabbed a bullhorn.

SOMERVILLE — US Senator Elizabeth Warren brought a box of doughnuts with her as she joined dozens of workers outside a Stop & Shop here as the strike against New England’s largest supermarket chain entered its first full day Friday.


Warren was asked by reporters what message she wanted to send to the owners of the supermarket chain, Netherlands-based Ahold Delhaize.

“Be fair,’’ said Warren, who is seeking the Democratic presidential nomination.

Warren was stepping into one of the largest labor disputes in recent years. Thousands of supermarket workers walked off the job Thursday afternoon, forcing the chain to temporarily close some stores. Some customers refused to cross picket lines.

The United Food & Commercial Workers union, which represents the 31,000 workers on strike, called the work stoppage for 1 p.m. shortly after contract negotiations hit an impasse over pension and health benefits. Workers in three states had voted to authorize a strike in late February, but the employees only learned about the union’s directive to walk off the job about 15 minutes before it started.

Stop & Shop said it had a contingency plan in place for its 240 stores in Massachusetts, Connecticut, and Rhode Island.

Stop & Shop is the only major chain in the region with a largely unionized workforce. It faces increased competition from rivals with lower labor and operating costs, while its workers have been emboldened by recent strikes in other industries in which teachers and hotel workers have come out on top.


Stop & Shop has more than 400 stores in five states, and 60,000 employees. The stores in New York and New Jersey were not affected by the strike. Stop & Shop’s parent company, which also owns Hannaford and Food Lion, reported $2.1 billion in profits in 2018.

Meanwhile, some employees said they were making little more than $12 an hour, while others said they earned around $20 an hour. The company says that the average hourly wage is $21.30, with front-end clerks averaging $15.90, and other line workers making in the $18-$20 range.

Deliveries from the Peapod service are expected to continue, the spokeswoman said Thursday.

However, Teamsters Local 25, which represents other Stop & Shop employees who are not on strike, including warehouse employees and mechanics, as well as truck drivers who deliver to the store, has pledged to honor the picket line, raising questions of whether new stock will get to stores if there is an extended shutdown.

Despite a crowded field, Stop & Shop remains a formidable competitor in New England. It has more than one-fifth of the grocery market in the eastern half of New England, according to Shelby Publishing Co., owner of The Griffin Report of the Northeast, which follows the supermarket industry. It’s even more dominant in western New England, with 40.7 percent of the market.

Meanwhile, public sympathy for striking workers is higher than it has been in the past, said Steve Striffler, director of the Labor Resource Center at the University of Massachusetts Boston. Public school teachers in multiple states went on strike over the past year, and 7,700 Marriott workers in eight cities, including Boston, went on strike simultaneously last fall.


John R. Ellement can be reached at ellement@globe.com. Follow him on Twitter @JREbosglobe. Katie Johnston can be reached at katie.johnston@globe.com. Follow her on Twitter @ktkjohnston.