Boeing bargained in good faith with one of its biggest unions for the new labor contract and "did not hold back with an eye on a second vote", its chief operating officer said on Tuesday in a letter to employees seen by Reuters.

A tentative deal with The International Association of Machinists and Aerospace Workers (IAM) has upset many workers who were hoping for higher wage hikes and better pensions, its lead negotiator, Jon Holden, told Reuters on Monday.

Boeing workers listen to union leaders speak as Boeing's Washington state factory workers vote on whether to give their union a strike mandate as they seek big salary gains from their first contract in 16 years, at T-Mobile Park in Seattle, Washington, U.S. July 17, 2024. REUTERS/David Ryder

In the letter, COO Stephanie Pope reiterated "unprecedented commitment" to the terms of the proposed deal, which include a general wage increase of 25% and a commitment to build its next commercial airplane in the Seattle area.

Holden said many members wanted to hold out for a 40% pay rise over the contract period and a reinstatement of the defined-benefit pension plan they reluctantly gave up during a round of negotiations a decade ago.

If the union workers vote down the deal and decide to strike, it would be a blow to new Boeing CEO Kelly Ortberg, who took up his role last month with a mandate to improve safety and ramp up production of the company's best-selling 737 MAX passenger jet.