The union representing 31,000 Stop and Shop employees said it reached an agreement with the company April 21, putting an end to a strike that started April 11.

The workers, all located in the Northeast, walked off the job after both sides were unable to come to an agreement on healthcare and retirement benefits. Health-care plans and pensions are maintained under the new agreement, the union said.

Five United Food and Commercial Workers locals represent the employees.

The company said that it was “very pleased” with the three-year tentative agreement which now has to be ratified by members.

“Under this...