The union says its members have gone without a pay rise for four years
Production at the world's biggest aircraft manufacturer, Boeing, has halted in the US after 27,000 workers at the company went on strike over pay.
Members of the Machinists Union, mainly based in Seattle, downed tools after last minute negotiations failed.
Boeing says it has offered more than $34,000 (£19,200) per employee in pay and benefits.
Analysts say the stoppage will cause further delays in the delivery of the new Dreamliner aircraft.
The union says with that with Boeing's record profits and its members going without a pay rise for the last four years, the offer is not good enough.
The BBC's Matthew Wells said no further talks were scheduled between unions and management at this stage.
Union members hoisted their strike signs outside the Boeing plant in Everett, a city north of Seattle, cheering and blasting air horns at passing cars.
Striking workers were told by one union member that they would not falter on the strike.
"We will show the company that they are going to have to go back and bargain in good faith," said the unnamed man. "And we will stay out until every single member gets something in their contract", he told a cheering crowd of workers.
A Boeing spokesman, Tom Healy, said the company was open to further discussions.
"We've bargained in good faith, we've worked hard, but we've not been able to close the gap," said Mr Healy. "We've not been able to come close on an agreement."
The Machinists Union is Boeing's biggest labour group, and the company has said it will not try to assemble aircraft during the strike.
Analysts say that the stoppage could cost Boeing at least $100m each day in lost revenues - as well as delays in delivering the Dreamliner.
Boeing hopes that its latest lightweight passenger jet - which is already two years late - will help it compete with rival manufacturer, Airbus.
Most of the striking workers are based around Seattle in Washington State.