Global ratings agency S&P said on Tuesday it had placed Boeing's rating on CreditWatch negative as about 33,000 of the U.S. planemaker's workers remain on strike, halting production of its best-selling jets.

S&P Global Ratings is looking at downgrading Boeing Co.’s credit grades to junk, citing the planemaker’s growing cash needs as it suffers from a strike by machinists that looks increasingly likely to wear on.

Boeing Co. is on the verge of a significant financial setback as S&P Global Ratings considers downgrading the company’s credit rating to junk status. This looming downgrade is driven by Boeing’s escalating cash requirements and the prolonged strike by machinists that has severely impacted the company’s production capabilities.