The union that includes Island Stop & Shop employees voted on Sunday to authorize a strike as part of contract negotiations with the company.

Employees are still at work at the two stores in Edgartown and Vineyard Haven and negotiations remain ongoing; the vote confirms readiness to stop working if union leaders call on them to do so.

Negotiations between the grocery chain and five local union branches began in January. The previous three-year contract expired Feb. 23. The five union branches represent 31,000 workers in Massachusetts, Rhode Island and Connecticut. All five have authorized a strike.

Vineyard Stop & Shop employees belong to the Local 328 branch of the United Food and Commercial Workers (UFCW) union, which is based in Rhode Island and includes Southeastern Massachusetts and two stores in Connecticut. According to union leadership, there are 117 union workers at Martha’s Vineyard Stop & Shop stores.

The vote to authorize a strike took place at a meeting Sunday in Foxboro. Island workers held a separate meeting at the Barn and Bowl in Oak Bluffs. Union president Tim Melia said wages, health care and pension are sticking points.

“People are upset. They’re united. They’re very united. We had a great turnout yesterday. It was beyond my expectations,” Mr. Melia said of the Foxboro meeting. “It shows that people are upset not just about contract proposal, but about the way they have been treated by the company in the last three years.”

He said employees have expressed concerns about automation with self scanners, bagging carousels instead of baggers, even a clean-up robot being tested at some stores.

“The hours are getting cut. They’re expecting people to do more with less,” Mr. Melia said.

The last time the union authorized a strike was six years ago. Workers have not actually gone on strike in 30 years, Mr. Melia said.

A statement from Stop & Shop notes that the company is the only fully-unionized store in New England. The company has also cited competition with other chains like Walmart and Whole Foods and online marketplaces like Amazon as a factor affecting stores.

“We are proud of our relationship with associates and optimistic that we will be able to reach new agreements,” the company said in a statement.

More negotiations are scheduled for March 13 and 14.