On June 11, NStar employees will vote on a proposed contract that NStar and union officials agreed upon 15 minutes before their deadline at midnight Friday.

The contract comes after weeks of negotiations over provisions on job security, working conditions, and health care.

“The medical was an issue and we came to an agreement on that,” said Dan Hurley, the president of the Utility Workers Union of America Local 369. “There were a lot of issues there yesterday morning, but we worked through them.”

NStar officials said key provisions include yearly salary increases, a choice among three medical dental, and vision plans, and keeping the company’s call center in Westwood.

Hurley said union officials are still informing NStar employees of the provisions and will not release more details of the contract at this time.

“Our job is to negotiate the best deal that we can. The rest is up to our members,” Hurley said.

NStar is the largest electric and gas utility company in Massachusetts and employs about 1,850. Hurley said union contract negotiations are increasingly tense because companies are paying their executives millions of dollars while trying to cut workers’ salaries and benefits.

Also on Saturday, workers at the Pilgrim Nuclear Power Station in Plymouth, also part of the union, rejected their proposed contract, according UWUA Local 369. The union makes up about 90 percent of the plant’s workforce. The union and the plant’s owner, Entergy Corp., will try to work out a new agreement by Tuesday, when the current contract is set to expire.

Meanwhile, NStar submitted a 76-page report, written by an independent agency, to the city of Boston and state Department of Public Utilities explaining that a March blackout in Back Bay was caused by a ruptured transformer cable connector. The rupture then sparked a fire, which was fueled by mineral oil in the cable.