Boeing didn’t disclose how many planes were affected and said it was too early to know how long it would take to inspect the planes, ensure that the affected part is correctly installed and make any required fixes.

The electrical issue relates to a component unrelated to the automated flight-control system malfunction that led to the crashes of planes flown by Indonesia’s Lion Air in October 2018 and Ethiopian Airlines in March 2019, according to a Boeing spokesperson. Boeing shares were down 1.3% in early trade.

American Airlines Group Inc.

AAL -0.56%

said it was notified of the potential production issue with the electrical component on Thursday night. The airline said it took 17 of its most recently delivered MAX aircraft out of service to complete necessary inspections. American still has 24 other MAX jets in its fleet that it said were produced before the plane was recertified by regulators last year.

David Seymour,

American’s chief operating officer, wrote in a message to employees Friday that Boeing had traced the issue to a production change made in the installation process that occurred after American had received its last aircraft before the March 2019 grounding. “We will never knowingly operate an aircraft with a known or potential issue,” he wrote, though he said that there would be some operational challenges, such as rerouting crew members and changing schedules.

Southwest Airlines Co.

LUV -0.69%

said 30 of its 58 MAX jets were affected and had been removed from flying, but didn’t expect its operations to be affected as the pandemic-driven travel slowdown has left it with surplus jets.

United Airlines Holdings Inc.

UAL -1.73%

said it was taking 16 MAX jets out of service, out of the 30 it has in its fleet. The airline said it was working to cover the flying with other planes and didn’t have an estimate of when it would be able to bring back the affected MAX jets.

Alaska Air Group Inc.

ALK -0.69%

said it had taken all four of its MAX jets out of service for inspection, at Boeing’s recommendation.

More than 100 MAX jets have re-entered service since regulators cleared the plane to restart commercial service, with Boeing working through a backlog of 450 undelivered jets as well as more than 380 operating when regulators grounded the global fleet.

Boeing on Friday said it is working with the Federal Aviation Administration on resolving the issue and was continuing production of the MAX. The FAA said in a statement that it would ensure the issue was addressed.

—Dave Sebastian contributed to this article.

Write to Alison Sider at alison.sider@wsj.com and Doug Cameron at doug.cameron@wsj.com