LOS ANGELES, Sept. 8 (Xinhua) -- About 27,000 machinists who assemble commercial aircraft in Boeing's factories across the United States Monday walked off assembly lines after talks on a new labor contract failed and their union called a strike.

    Members of the International Machinists and Aerospace Workers overwhelmingly voted to authorize a strike last week, but agreed to delay the work stoppage for two days as Boeing said it would change the contract offer through negotiations.

    The strike formally began midnight Friday after a last-ditch negotiation effort between union leaders and Boeing executives, which was brokered by Washington State Governor Chris Gregoire and a federal mediator, failed.

    Monday's strike closed down assembly lines for Boeing 737, 747,767, and 777 jetliners in Boeing factories in Seattle, Oregon and Kansas. Union leaders said there would be no further talks with the company.

    "We will continue this fight 'one day longer' than the company can afford until they meet our demands," the union told its members late Sunday on its Web site.

    It seems that the strike will inevitably delay Boeing's deliveries of its aircraft, and the company said it was talking with customers regarding the strike's impact.

    Boeing had offered to raise wages by an average of 11 percent over three years and boost the pension multiplier by 14 percent for the workers. But the union insisted the demand for a general wage increase of 13 percent and better pension benefits.

    Last time the union went on strike for a month in 2005 before the company improved its offer to settle the labor dispute.