American Airlines has grounded 14 planes and canceled 40 flights Thursday because of an issue with overhead bins.

In a statement, the airline said an outside vendor updated the interiors of several Boeing 737-800 aircraft and after inspecting two of the planes, the airline found the work was "not up to our standards."

The airline said it decided to remove from service an additional 12 aircraft "out of an abundance of caution."

The airline provided no further details.

"We are working with our vendor and the FAA to immediately address this issue," the statement said.

Gary Schaible, president of the Transport Workers Union Local 591, said it's a safety issue.

"They don't take planes out of service for cosmetic reasons," he said.

The issue involves overhead bins "popping open continuously" and problems with a battery cable that runs along the bins that was improperly installed and could chafe and catch fire, Schaible said.

He added that the work being done on the bins was part of a project to add more seats to the planes.

The union, which represents 4,000 mechanics and 800 other workers, has often raised safety questions about maintenance work that is "outsourced" to private vendors.

"Our mechanics would never allow this to happen," Schaible said.

The union even started a website about safety issues aimed directly at passengers.

The pilot's union echoes the mechanics' concerns.

"Ironically in the most profitable times in airline history, we see a continuation of the drive to pinch pennies and go through outsourcing," said Capt. Dennis Tajer, a spokesman for the Allied Pilots Association. "This outsourcing is outrageous."

In a statement, the FAA said it was aware of the airline's decision to ground the planes.

"We are in contact with the carrier and will monitor the situation," the FAA said.

American, meanwhile, said "we never want to disrupt our customers’ travel plans, and we are sorry for the trouble this has caused. Our team has rebooked all customers that were impacted by nearly 40 flight cancellations thus far and will continue to work proactively to get our customers to their final destination."

The airline noted its contractor is a longtime FAA-licensed vendor.

Aviation Technical Services, based near Seattle, confirmed it was the vendor involved.

"We are working closely with our customer, American Airlines, to identify and resolve the issue," ATS said in a statement.