Bath Iron Works and its largest union exchanged Wednesday letters showing a lingering stalemate during a strike over subcontractor and seniority provisions in the shipyard’s last contract offer.

It was the first formal exchange between the two parties since the International Association of Machinists and Aerospace Workers Local S6, which has about 4,400 of the total 6,600 workers at the Navy contractor, voted Sunday to reject a three-year contract and strike for the first time in 20 years.

The two sides have been signaling their stances in the media. Jay Wadleigh, former president of Local S6 and the business representative for the union’s regional parent, on Monday said the union was willing to meet but that “ it’s their move,” referring to BIW. On Wednesday, BIW spokesperson David Hench volleyed back in a statement saying the company was willing to meet but “the ball is in their court,” meaning the union.

In a Wednesday letter to Wadleigh, reposted on the union’s Facebook page, BIW human resources director Jonathan Mason said BIW had read several statements in the press about the union’s willingness to return to the bargaining table, but “BIW has not heard from the union directly on this topic” and he “wanted to reach out to clarify where things stand.”

Mason said BIW’s offer had expired and the company did not have an alternative offer to present. He said BIW’s position on the primary non-economic aspects of its “last, best and final offer” had not changed.

The union’s main issues of contention in the proposed contract were BIW’s request to bring in subcontractors to catch up on work that is six months behind and the union’s desire to keep seniority preferences for its members. The expired contract proposal offered a 3 percent annual raise for each of the three years, but increased insurance copays and asked for BIW alone to determine when it hires subcontractors.

Wadleigh responded by saying the union’s position remains the same, but it is willing to meet and negotiate. His letter said “it is unfortunate that Bath Iron Works is not willing to review and revise its non-economic proposals,” he said, pointing out that 87 percent of the voting membership was against the contract and for a strike.

In an interview Thursday, Wadleigh said he has not heard back from the company.

“They’re not willing to talk about non-economic issues, which is why we are on strike,” he said. “This is not about economics, it’s about the entire contract.”

Wadleigh said Tuesday that he had talked to a federal mediator. A BIW spokesperson has not responded to requests for comment on whether the company also has talked to the mediator. The union’s strike committee plans to hold a solidarity supper on Friday from 6 p.m. to 9 p.m.