The largest union at Navy shipbuilder Bath Iron Works said Wednesday it could lose about 30% of its membership — or more than 1,000 workers — over the Biden administration's vaccine mandate for federal contractors.

Machinists Union Local S6 supports the COVID-19 vaccines but contends they shouldn't be required for workers. The union represents the shipyard's production workers, about 4,800 of the shipyard's 6,500 workers.

“We believe it is wrong to threaten someone’s livelihood over the vaccine at a time when valued workers are in such high demand while being deemed essential employees throughout this pandemic,” the union said.

All workers are needed to keep shipbuilding on schedule at a time when the Navy faces growing threats around the world, the union said.