While Bath Iron Works officials and leaders of the shipyard’s drafters union met Wednesday with a federal mediator in continuing efforts to negotiate a new four-year contract, union leaders told members Thursday morning that strike assistance personnel from the United Auto Workers and the Maine AFL-CIO were helping to prepare the local 3999 for a potential strike.

“We anticipate having UAW strike assistance personnel on site this evening and will be reaching out to those members who volunteered to assist in the event of a strike to begin more focused planning,” the local union posted on Facebook Thursday morning.

Members of the Bath Marine Draftsmen’s Association, Local 3999 of the International Union of United Automobile Workers, voted “overwhelmingly” on Sunday against the company’s “last, best and final offer,” and said they would prepare for a strike should continuing negotiations this week not succeed, according to union officials.

On Monday, the union, which represents about 700 of BIW’s approximately 6,000 employees, issued a statement on its Facebook page announcing that both parties had agreed to a one-week contract extension, with the company agreeing not to engage in a lockout before Sunday and the union agreeing not to strike before that date.

According to the contract extension agreement, signed by union and company officials, the existing collective bargaining agreement was signed Sept. 16, 2013, and expired Sept. 17, 2017. The extension expires at 12:01 a.m. Sunday.

The proposed contract would expire March 20, 2022, according to official documents.

A key issue is BIW’s proposal to eliminate most of the flexible schedule benefit, which union leaders say has benefitted members, Trent Velella, vice president of the union, said in a release Tuesday.

In a release Tuesday, the BMDA accused the company of engaging in “unfair labor practices.” Subsequent calls to union leadership have not been returned.

In December 2015, the largest union at Bath Iron Works — Local S6 of the machinists union — voted to accept a four-year contract that did not include pay raises but did offer annual bonuses.

On Monday, Lisa Read, a spokeswoman for General Dynamics, which owns Bath Iron Works, would only say that the company continues to negotiate with the union. Read said Tuesday that the company had no comment. She did not immediately respond to a request for comment on Thursday.