Just months after the Boeing 737 Max took the skies again, major airlines are taking some of the planes out of service.

Boeing is calling it a "production issue" and told 16 airlines to temporarily ground certain Max aircraft. The impacted airlines include Southwest, American and United, among others.

Boeing said the recommendation was made “to allow for verification that a sufficient ground path exists for a component of the electrical power system.”

The airline did not say how many planes were affected.

A spokeswoman from Southwest Airlines told USA Today they had removed 30 of its 58 Max aircraft from service. American says they have grounded 17 planes.

In a statement posted on Twitter, the FAA said they "will ensure the issue is addressed. Passengers should contact airlines about possible flight delays and cancellations."

The 737 Max was grounded in March 2019 after two deadly crashes that killed more than 340 people. The FAA approved the fixes Boeing made to the safety system that was blamed for the crashes, and allowed the aircraft back in the sky.