(Reuters) -Boeing ( BA ) presented a new contract offer on Monday to the union representing more than 3,200 striking workers at its St. Louis-area plants, proposing a higher ratification bonus and other revisions in a bid to end the walkout.

The International Association of Machinists and Aerospace Workers represents members who assemble fighter jets and munitions at Boeing's ( BA ) plants in the St. Louis area.

In its updated offer, the planemaker raised the ratification bonus from about $3,000 to $6,000.

Boeing ( BA ), however, removed a retention bonus of $1,000 from its new offer to provide more cash upfront, it said.