(Reuters) -Boeing ( BA ) said on Tuesday that it had withdrawn its pay offer to around 33,000 striking U.S. West Coast factory workers and no further negotiations were planned with their union representatives.

"Unfortunately, the union did not seriously consider our proposals," Boeing Commercial Airplanes head Stephanie Pope said in a note to the employees, calling the union's demands "non-negotiable".

"Further negotiations do not make sense at this point and our offer has been withdrawn."

The union is seeking a 40% pay rise over four years and the restoration of a defined-benefit pension that was taken away in the contract a decade ago.

Boeing ( BA ) made an improved offer last month that it described as its "best and final", which would give workers a 30% raise and restore a performance bonus, but the union said a survey of its members found that was not enough.

The International Association of Machinists and Aerospace Workers union said in a statement that Boeing ( BA ) was "hell-bent on standing on the non-negotiated offer" proposed last month.

"They refused to propose any wage increases, vacation/sick leave accrual, progression, ratification bonus, or the 401k Match/SCRC Contribution. They also would not reinstate the defined benefit pension," it said.