A group of unionized Stop & Shop supermarket workers agreed to a three-year contract in the wake of an 11-day strike that cost the company as much as $10 million per day.

About 31,000 workers at 246 stores in Connecticut, Massachusetts, and Rhode Island walked off the job April 11. The strike ended late April 21 when management and union leaders announced they had reached a tentative agreement. Workers stopped picketing and began reporting to work April 22. Stores, which were either closed or largely empty during the strike, have started returning to normal.

And workers have begun ratifying the...