SOMERVILLE - U.S. Sen. Elizabeth Warren, a Massachusetts Democrat running for president in 2020, delivered donuts and coffee to picketing Stop & Shop workers in Somerville on Friday, and urged shoppers to take their business elsewhere.

“Do not cross the picket line,” Warren said. “Understand people on the picket line are not just fighting for their families. They’re fighting for all our families. They’re fighting for basic fairness and equality in this country.”

On Thursday, the unions representing 31,000 Stop & Shop workers across Massachusetts, Rhode Island and Connecticut voted to go on strike. Their contract expired in February, and they have been unable to reach a deal on a new one.

Warren shook hands with workers and encouraged them with a pro-union message.

“This is a company that made $2 billion in profits, that then got a fancy tax break in Washington from the Republicans and now wants to squeeze our workers right here in Massachusetts,” Warren told the workers. “Well, we’re not going to put up with it.”

Speaking to reporters, Warren reiterated the message that she has been campaigning on for years, that the wealthy are taking advantage of the working class. “This is the problem all across this country is that those at the top think that they can just keep sucking out every bit of profit and leave nothing for the working people, the people who actually get out there and make it happen every day,” Warren said.

“What people are asking for here is they’re just asking for fair wages, they’re asking for health care benefits and just as shot at a decent retirement,” she said.

Marc Perrone, the international president of United Food & Commercial Workers, said 243 Stop & Shop stores have shut down. Others, like the store in Somerville, are operating with limited hours and services.

Perrone said in an interview from the picket line that the biggest issue in negotiations is health insurance. Although the store offered a small wage increase, that would be more than outweighed by a proposed cut to health insurance benefits. “When you look at the total package, it was going to be less money in their pockets,” Perrone said.

Stop & Shop says employees’ health care premiums would still be below the national average and would increase by $2 to $4 a week. The wage package being offered is among the best UFCW retail contract in the country, according to the store. The company would continue to offer a defined benefit pension plan.

The exact contract being offered varies by union.

Kristen Johnson, a deli manager in Somerville and union shop steward, said she is particularly concerned about increased health care costs and changes the store is proposing for new hires.

“We’re asking our customers to please shop somewhere else until we’re back, until we have a fair contract,” Johnson said.

The UFCW locals are affiliated with the AFL-CIO. Steven Tolman, president of the Massachusetts AFL-CIO, said, “The goal is to have them come to the table with a reasonable process to be fair and equitable and have a little dignity for the employees.”