The White House said on Thursday it was encouraging Boeing and the union representing about 33,000 striking machinists to continue working to reach a deal, a day after workers rejected the planemaker's latest contract offer.

President Joe Biden "directed his team … to encourage parties to continue working to achieve an agreement that works, certainly for all parties," White House press secretary Karine Jean-Pierre told reporters. "We're going to continue to monitor those negotiations and continue to make sure that we encourage that."

Earlier on Thursday, the Labor Department said Acting Secretary Julie Su was in contact with Boeing and the International Association of Machinists and Aerospace Workers.

She was in Seattle twice last week to assist in contract talks that are aimed at ending a six-week strike that has halted production of Boeing's best-selling 737 MAX as well as 767 and 777 wide-body programs.

A spokesperson for Su said she "is available to support" Boeing and IAM.

The union said 64 percent of workers voted against the latest deal, which offered a 35 percent rise in wages over four years.

The rejection of Boeing's offer, which comes after 95 percent of workers voted against a first contract last month with a 25 percent pay hike, reflects years of resentment from workers and deepens a financial crisis at the company.

After the vote, union leaders said they were ready to immediately resume negotiations with Boeing.

The union has been seeking a 40 percent pay rise and the return of a defined-benefit pension.

Since the strike began on September 13, Boeing has announced plans to cut 17,000 jobs and is closing in on a plan to raise up to $15 billion from investors to help preserve its investment grade credit rating. Some airlines have had to trim schedules due to aircraft delivery delays.