BOSTON (CBS/AP) — Stop & Shop supermarkets in Massachusetts, Rhode Island and Connecticut are now being staffed by corporate and temporary workers while tens of thousands of employees strike outside the stores over stalled contract negotiations.

United Food & Commercial Workers union members from several locals walked off the job Thursday, with some customers saying they were told to leave their groceries behind and exit stores.

Employees are unhappy with the company’s proposed changes to retirement plans and health insurance, as well as the addition of self-checkouts and robots in stores. The union is asking people not to shop at the chain.

“The men and women who make Stop & Shop a success have earned and deserve affordable health care, a good wage, and the ability to retire with dignity,” the leaders of five locals said in an emailed statement. “They have earned and deserve a good job that allows them to do what they do best: provide the very best customer service for New England communities.”

More than 31,000 employees authorized union leaders to call for a strike. Quincy-based Stop & Shop, a division of Dutch supermarket giant Ahold Delhaize, has 415 stores across the Northeast but the strike affects 240 stores in the three states.

Stop & Shop spokesperson Jennifer Brogan told WBZ-TV Friday the majority of those 240 stores remain open, with most operating on modified hours from 8 a.m. to 8 p.m. All banks and pharmacies in the stores are open, but all gas stations will remain closed.

Stop & Shop said in a statement posted on its website that it was disappointed with the strike given that negotiations are ongoing with the assistance of federal mediators. The company added that management’s “reasonable” offer includes across-the-board raises and health and pension benefits it says are better than most other food retailers.

On Friday night, Stop & Shop CEO Mark McGowan sent a letter to employees, which said, in part, “Our team is standing by and remains ready to continue negotiations anytime. We hope that the UFCW local unions return to the table to reach a fair and responsible contract now. As a 28-year veteran of Stop & Shop, I want you to know how much I care about our associates. I stand behind the comprehensive offer we have placed on the table.”

The unions say the company is demanding “unreasonable” wage and benefit cuts.

“Instead of a contract that recognizes the value and hard work that our members provide every day, Stop & Shop has only proposed drastic and unreasonable cuts to health care benefits and take home pay, while replacing real customer service with more serve-yourself checkout machines,” the union statement said.

The unions said that Ahold Delhaize had more than $2 billion in profits last year and got a U.S. tax cut of $225 million in 2017.

“We’re disappointed that from day one they didn’t bargain in good faith with us. we’re disappointed that the hard workers are out here on a picket line instead of in the store serving their customers. We support out customers. and our customers support us. and again, we’re going to stay out here as long as we have to to get a fair contract,” Joe Villanucci, the union shop steward at the Medford store, told WBZ-TV Friday.

Paul Tritto, a worker on strike explained, “With the proposal, they have with healthcare and time and a half on Sunday, they take that away from me, they’re going to take $300 out of my pocket every week. That’s a part-time job.”

Worker Roberta Breen said, “It’s been hard I’ve been here for ten years. Our customers are like family to us and they feel the same.”

“They’re stubborn, but we’re more stubborn,” said worker Kristen Johnson.

Senator Elizabeth Warren greets striking stop and shop workers In Somerville.#wbz pic.twitter.com/y7YUxj4Uib — Beth Germano (@BethWBZ) April 12, 2019

In the end some customers stayed away. “It’s a bummer that the store’s closed,” said one Somerville customer. “But they just have to do what they have to do.”

Other customers went in and were treated to shouts as they left the store with food. But one Somerville customer said the location is the most convenient for her.

Massachusetts Senator Elizabeth Warren, who is running for the Democratic nomination for president in 2020, visited the Stop & Shop in Somerville Friday and brought striking workers donuts at the picket line.

“Stop and Shop makes billions in profits then turns around and wants to squeeze its workers,” she said to the gathering.

(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)