Boeing is offering its staff a 25% pay increase over a four-year contract to avoid the looming strike on Friday that could potentially shut down its assembly lines.

Union leaders representing more than 30,000 employees have urged the workers to support the proposal, describing it as the best contract they had ever negotiated.

According to BBC, if the agreement is approved, it would be an important achievement for Boeing’s new chief executive, Kelly Ortberg, who faces pressure to fix the company’s quality and reputational issues.

Boeing workers in the Seattle and Portland region are set to vote on the deal on Thursday. A strike can still happen if two-thirds of union members support it in a separate vote.

In a video message to Boeing workers, the aerospace giant’s chief operating officer, Stephanie Pope, described the proposal as a “historic offer.”

If ratified by union members, it would be the first full labor agreement between the firm and the unions in 16 years.

In a statement, the International Association of Machinists and Aerospace Workers (IAM) says that although the tentative deal did not match the union’s initial 40% pay raise target, negotiators still praised it and advised members to accept it.

“We can honestly say that this proposal is the best contract we’ve negotiated in our history,” read the statement.

In addition to the pay bump, the deal offers workers improved healthcare and retirement benefits and Boeing's commitment to building its next commercial airplane in the Seattle area.

It also gives the union members more say on safety and quality isues.