DALLAS/NEW YORK/CHICAGO ¨C Boeing Co.¡¯s credit rating is at risk as the grounding of the company¡¯s 737 Max jetliner drags into a fifth month, with Moody¡¯s Investors Service joining Fitch Ratings in sounding a warning.

The plane maker faces a $5 billion cash-flow drain this year as it continues to churn out aircraft it can¡¯t deliver until regulators around the globe clear the Max to resume commercial flights, Moody¡¯s said in a statement Monday. Like Fitch, Moody¡¯s affirmed Boeing¡¯s rating at the sixth-highest level of investment quality while cutting the outlook to negative.

¡°Financial risk relative to the company¡¯s pre-grounding profile has meaningfully increased, and the resolution and ultimate impact for Boeing, both financially and reputationally, remain unknown,¡± Moody¡¯s said.

The grounding of Boeing¡¯s best-selling jet will clip operating margins for years to come, while posing a significant public-relations challenge that will linger into next year and beyond, Fitch said earlier in the day. Uncertainty around the return to service of the Max and the ¡°growing logistical challenge¡± of getting parked planes back in the air threaten Boeing¡¯s credit, Fitch said. There¡¯s also a risk that the company will have to make costlier concessions to airlines.

Boeing¡¯s bonds were unchanged after the Fitch and Moody¡¯s reports. The cost to protect its debt against default for five years rose 1.6 basis points, according to data provider CMA.

The manufacturer¡¯s benchmark 10-year bond has traded higher since the March 10 crash of an Ethiopian Airlines jet, the second Max accident in a five-month span. The notes were last quoted at 103 cents on the dollar, according to Trace. Boeing was able to sell $3.5 billion of new debt in April, boosting the size of the transaction amid strong demand.

The shares fell 1 percent to $373.42 at the close in New York.

Regulators around the world banned the Max from flying in March after the Ethiopia crash. A total of 346 people died in the two accidents.

Boeing last week disclosed a $4.9 billion after-tax charge to cover potential consideration for Max customers forced to cancel thousands of flights or line up replacement aircraft.

S&P Global Ratings said last week that the charge, which is $5.6 billion on a pretax basis, wouldn¡¯t affect Boeing¡¯s credit ratings. But S&P warned that more damaging effects to the company¡¯s finances or a ¡°substantial loss¡± in market share to the 737 could warrant a downgrade.

Like S&P, Fitch rates Boeing as an A. Moody¡¯s grades it at an equivalent level of A2.