Boeing has announced a new problem with its 737 MAX that will ground some of the jets again.

"Boeing has recommended to 16 customers that they address a potential electrical issue in a specific group of 737 Max airplanes prior to further operations," the company said on Friday.

It wants 16 of its customers to check and verify "that a sufficient ground path exists for a component of the electrical power system."

The 737 MAX returned to service in November after a 20-month safety ban that was triggered by two fatal crashes that killed 346 people.

A Boeing spokeswoman said by email that this issue was not related to a key safety system called MCAS, which had led to the wider safety grounding.

"We are working closely with the U.S. Federal Aviation Administration on this production issue," the company said in a statement on Friday.

"We are also informing our customers of specific tail numbers affected and we will provide direction on appropriate corrective actions."

Southwest Airlines said 30 of its 58 737 MAX 8 aircraft, a variant of 737 MAX, were affected by Boeing's notification. The airline will swap any flights previously scheduled with the aircraft with other planes in its fleet.

Production defects with Boeing's larger 787 Dreamliner planes had also spurred a broad review by the U.S. Federal Aviation Administration, which last month decided to independently handle final pre-delivery checks on four 787 jets.

Boeing was forced to stop deliveries of the 787 jets for several months due to production problems and only resumed them late last month.

(With input from Reuters.)