The crisis engulfing Boeing Co. took a dramatic turn after negotiations to resolve an almost monthlong strike collapsed and S&P Global Ratings warned it may cut the planemaker’s credit grade to junk.

Both the embattled company and the International Association of Machinists and Aerospace Workers blamed each other for the impasse. Boeing said the union made “non-negotiable demands,” while the IAM said the company was “hell-bent on standing on the non-negotiated offer.”

The impasse leaves Boeing with no clear path forward to overcome the debilitating strike, which has shut down production at its key commercial manufacturing base on the US west coast. Even before talks broke down, S&P highlighted the urgency to reach a resolution by pointing to an estimated $10 billion cash burn this year that will likely require additional funding to cover day-to-day cash needs and debt maturities.

“Unfortunately, the union didn’t seriously consider our proposals,” Stephanie Pope, who runs Boeing’s commercial airplane unit, said in a memo shared by the company. “Instead, the union made non-negotiable demands far in excess of what can be accepted if we are to remain competitive as a business.”

Boeing shares fell 1.5% in premarket US trading on Wednesday. The stock has declined 41% this year, sheddding more than $60 billion in market value as the company bounced from crisis to crisis.

Boeing’s now-withdrawn contract proposal, made two weeks ago in a direct approach to workers, offered to hike wages 30% and boost retirement benefits.