BATH, Maine (AP) The largest union at Navy shipbuilder Bath Iron Works begins voting Friday on a contract proposal that was unanimously rejected by its negotiating committee.

That raises the possibility of the first strike in 20 years.

Shipbuilders from Machinists Union Local S6 would see a 9% pay raise over three years under the proposal, but they’re digging in over what they view as concessions on subcontracting, work rules and seniority.

Workers will be voting from Friday through Sunday at noon, ahead of the contract expiration.

The last strike at the shipyard, in 2000, lasted 55 days.