Negotiators for Bath Iron Works’ largest union reached an agreement with shipyard officials on a new contract Tuesday night.

The proposed four-year agreement will be presented to the 3,600 members of Machinists Union Local S6 on Sunday during a vote at the Augusta Civic Center.

Local S6 President Jay Wadleigh declined to divulge contract details before union members are given letters on Wednesday that explain the proposal’s impact on their jobs and working conditions.

The current contract doesn’t expire until May. Wadleigh said it was BIW management that requested an early start to negotiations, a step that BIW felt would give it time to position itself to bid on Coast Guard offshore patrol cutters in March. He said negotiations began Nov. 16.

Shipyard workers already have been warned that 20 percent of the workforce could be eliminated if BIW, a subsidiary of General Dynamics, fails to win the Coast Guard contract. Bath Iron Works hasn’t built a Coast Guard vessel since the 1930s but hopes to outbid two Gulf Coast shipyards for a project with an estimated value of $10 billion.

The union agreed to open negotiations last month, realizing that doing so might give the shipyard a competitive advantage.

“Both sides want the Coast Guard contract,” Wadleigh said. “Whether the members will ratify the (labor) contract is another question.”

Defense analysts say the Coast Guard is serious about cutting costs and will go with the lowest-cost option regardless of which shipyard it might be.

“General Dynamics management and its labor unions understand that in the end, they have to get along because if they can’t, nobody’s going to save them,” Loren Thompson, a defense analyst at the Lexington Institute, told The Associated Press. “The Navy and the Coast Guard are looking for the best deal possible. Given some of the disadvantages that Bath has in terms of location, they need to have a unified team to win future programs.”

The company invoked a clause this year in the current contract that calls for an early review of the existing contract, according to the AP.

If members do ratify the new contract Sunday – Wadleigh is calling it a contract extension – components of the contract will be phased in over the next several months, with the extension expiring on May 22, 2020.

At a ship christening ceremony in Bath last month, BIW President Fred Harris told the crowd that the Navy is buying fewer ships and demanding that they be built more affordably. Harris said the competition for shipbuilding contracts has never been more intense.

Relations between labor and management at BIW have been strained for months, since officials proposed outsourcing some fabrication jobs now done at the shipyard. The two sides have been in arbitration over the issue.

Although there has been no talk of a strike this year, Local S6 was involved in the last major strike at the shipyard, which lasted for 55 days in 2000.

BIW is one of the state’s largest employers, with a workforce that exceeds 5,700 people.