* Boeing workers to decide on strike mandate

* Union seeks 40% raise in first full negotiation with Boeing in 16 years

* Boeing faces financial and production challenges, including competition from Airbus

(Recasts to reflect that voting has begun, adds comment from Boeing worker, details from union event, paragraphs 10-12)

SEATTLE, July 17 (Reuters) -

Boeing's Washington state factory workers are voting on Wednesday on whether to give their union a strike mandate as they seek a 40% raise in their first full negotiation with the planemaker in 16 years.

Many of the estimated 30,000 workers who build Boeing's 737 MAX and other jets crowded to vote at Seattle's T-Mobile Park, although they cannot strike before their contract expires on Sept. 12.

Boeing's labor talks come as the U.S. planemaker loses ground to rival Airbus and navigates a crisis that erupted after a door plug blew off an Alaska Airlines 737 MAX jet in mid-air on Jan. 5. The planemaker also faces other issues.

"We remain confident we can reach a deal that balances the needs of our employees and the business realities we face as a company," Boeing said in a statement regarding the Washington labor talks.

While the vote on Wednesday is considered procedural, the union kicked off the 12 p.m. PDT event with music, speeches and an earlier convoy of workers on hundreds of motorcycles.

“It does empower the negotiating committee, it does send a strong message," union local president Jon Holden said about the vote during a June interview.

For example, the vote would free up funds in case members choose to strike later, he added.

North American unions have capitalized on tight labor markets to win hefty contracts at the bargaining table, with airline pilots, autoworkers and others scoring big raises. The International Association of Machinists and Aerospace Workers (IAM), which represents the Boeing workers, has said the company's financial and production challenges will not change its workers' readiness to strike if needed.

Aerospace mechanic Heath Hopkins said many of the workers, who are concerned about pensions and other issues, have been yelling and banging on materials inside their factories to raise awareness.

“It gets noisy in my shop every hour," Hopkins said on the sidelines of the Wednesday event. "You have to put ear plugs in."

“It’s basically everyone in the shop showing that we are together as a union, as a group. We are ready to strike if we need to.”

Boeing has more than 66,000 employees who live and work in Washington state on programs like the MAX, 767 and 777 widebody jets, representing the largest percentage of the company's global workforce.

Boeing recently said it would plead guilty to criminal fraud conspiracy to resolve a U.S. Justice Department investigation linked to two 737 MAX crashes from 2018 and 2019 that killed a combined 346 people, the government said in a court filing earlier this month.

The U.S. planemaker, which has announced a deal to acquire key supplier Spirit AeroSystems for $4.7 billion, is expected to burn rather than generate cash in 2024.

(Reporting by David Ryder in Seattle and Allison Lampert in Montreal Editing by Matthew Lewis)