Boeing locked out 125 unionized firefighters and emergency responders from their jobs in Washington state this weekend as the two sides battle over a new four-year contract.

The aircraft manufacturer and the workers union, the International Association of Fire Fighters Local I-66, have been negotiating since February. Boeing forced the workers out early Saturday morning after the union turned down the companys final offer.

The union accused the embattled plane-maker of choosing corporate greed over safety, while Boeing insisted that it had a plan to ensure safe operations at the impacted manufacturing sites across the Puget Sound area.

We have now locked out members of the bargaining unit and fully implemented our contingency plan with highly qualified firefighters performing the work of [union] members, Boeing said in a statement.

A lockout is essentially the opposite of a strike rather than workers walking off the job by choice, an employer forces them off the job with the aim of gaining leverage in negotiations. Like strikes, lockouts tend to happen when a collective bargaining agreement has expired and a new one hasnt been reached.

The union said the lockout was intended to punish, intimidate, and coerce its firefighters into accepting a contract that undervalues their work.

When is Boeing going to make safety a priority? When is Boeing finally going to listen? Casey Yeager, the unions president, said in a statement.