The aerospace manufacturer withdrew its latest offer to a union whose more than 33,000 members went on strike last month, and both sides exchanged blame for the breakdown.

As the Boeing (BA) machinist strike threatens to drag into its fourth week with no end in sight, it remains unclear where things go from here. The company is losing hundreds of millions of dollars in badly needed cash,

"The union made non-negotiable demands far in excess of what can be accepted if we are to remain competitive as a business," the U.S. aerospace giant said in an email to employees late Tuesday.