Despite a 48-hour contract extension, negotiations between Boeing Co. and Machinists union officials have failed and the union declared: "The strike is on!"

The Machinists bargain for about 25,000 aircraft assembly workers in the Puget Sound area and about 2,000 more in Wichita, Kan., and Portland, Ore.

Picket lines went up early Saturday in Wichita, and West Coast machinists were due to walk out at 12:01 a.m. PDT.

This is the Machinists' second strike in as many contract negotiations. They struck for 24 days in 2005.

The company said it would not try to assemble planes during the strike.

Boeing spokesman Tim Healy said the company is open to further discussion, but both sides were too far apart to reach agreement. He added no additional talks were scheduled.