CHICAGO (Reuters) - American Airlines Group Inc grounded 14 Boeing 737-800 airplanes on Thursday after complaints by pilots that overhead bins on some recently-retrofitted aircraft cabins were not closing, an American official said.

FILE PHOTO: An American Airlines Boeing 737-800 airplane takes off at Simon Bolivar International Airport in Caracas, Venezuela January 25, 2019. REUTERS/Andres Martinez Casares

In a statement, American said the issue did not jeopardize the safety of flights and that it is working with the supplier that handled the cabin retrofits and the Federal Aviation Administration to immediately address the issue.

American had hired a long-time supplier, ATS, to update the main cabins of some of its 737-800s with 12 additional seats, said Gary Schaible, president of Transport Workers Union Local 591, which represents 4,800 American mechanics.

After write-ups from pilots saying that overhead bins on some 737-800s were not closing after the updating, the planes were taken to American’s maintenance base in Tulsa, Oklahoma, where mechanics discovered additional issues, Schaible said.

The American official confirmed the problem of bins not closing.

“After further inspection by American, the work that was conducted on these two aircraft was not up to our standards. Out of an abundance of caution, we have proactively removed from service the additional 12 aircraft that were updated by this vendor and have notified the FAA,” American said.

American, the world’s largest air carrier, has rebooked all customers on 40 canceled flights so far as a result of the groundings.

The airline has completed around 70 retrofits of the 737-800s, the American official said, but only around 15 were done by ATS, with the remainder handled in-house and by a separate supplier.

The company has not had an issue with any of the other updated planes, the official said.

The outsourcing of maintenance work, to U.S.-based suppliers like ATS or in-house American employees abroad, is at the core of ongoing contract talks between American and its mechanics unions.