Boeing Co. on Friday told 16 airlines to temporarily ground some of its 737 MAX aircraft due to a potential electrical issue.

The move comes less than four months after the Federal Aviation Administration approved the 737 MAX to fly again after the plane was grounded for almost two years following two separate crashes that killed more than 340 people.

Of the 16 airlines told to ground certain models of the 737 MAX, four were U.S.-based – American, United, Southwest and Alaska.

The FAA, in a tweet, said it was aware of Boeing’s latest issue.

Southwest Airlines, the largest U.S. operator of the plane, told USA Today it has not experienced any "operational challenges'' related to the electrical issue but has removed 30 of its 58 Max aircraft from service, according to spokeswoman Brandy King.

She said passengers due to fly on the grounded planes will be accommodated on other Boeing 737s in its fleet. Southwest only flies Boeing 737s.

"Southwest anticipates minimal disruption to our operation,'' King said in a statement.

American Airlines spokesman Curtis Blessing said, “As we shared when we returned the 737 MAX to commercial service, the safety of our customers and team members comes above all else. It’s with this unequivocal standard that we rigorously maintain and monitor all our aircraft — including the Boeing 737 MAX — to ensure every plane in the air is safe."

United removed 16 of its 30 737 Max planes, according to a statement. Alaska also removed four of its MAX 737-9.

"We have been in touch with the FAA and Boeing and will continue to work closely with them to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service,'' United said in a statement. "We are working to swap out aircraft to minimize the impact to our customers.''