American Airlines, the world's largest carrier, pulled 14 of its 304 Boeing 737-800s from service Thursday after finding a contractor failed to properly secure overhead bins on at least two planes. Forty flights were canceled as a result.
American mechanics had raised concerns after inspecting a plane that arrived at American's maintenance hub in Tulsa, Oklahoma. Sources told CBS News mechanics noticed hundreds of potential issues with modification work, including to electrical wiring. Mechanics said they feared some of the work created a potential fire danger.
Aviation Technical Services (ATS), which does contract work for American and other airlines including Southwest, had recently updated the interiors of the planes where the issues with the overhead bins were found as well as the 12 other aircraft taken out of service Thursday, according to American.
In addition to installing larger overhead bins on American Airlines' 737s, ATS installed new seats that include power outlets. The airline is now checking all of the modification work done on the 14 Boeing airliners.
American has contracted with ATS — an Everett, Washington-based FAA-licensed vendor — for several years.
American and its mechanics are locked in contract negotiations.
In a statement Thursday, American said "safety is our number one priority and is always at the forefront of all that we do." It also apologized to customers "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," it added.
The FAA told CBS News, "We are in contact with the carrier and will monitor the situation."
ATS did not immediately respond to CBS News' requests for comment.
Megan Towey contributed to this report.