Boeing is offering its staff a 25% pay rise over four years in a bid to avoid a strike that could potentially shut down its assembly lines as early as Friday.

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.

If approved, the agreement 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.