FORT WORTH, Texas (AP) — Federal officials say that American Airlines "may have" violated maintenance rules and they are continuing to investigate a union group's allegations that mechanics were pressured to clear planes for flying before it was safe.

The Federal Aviation Administration says it is continuing to investigate American's decision to remove inspectors and quality-control duties from some maintenance checks on large, two-aisle jets.

An FAA manager made the comments in a letter to Local 591 of the Transport Workers Union, which posted the letter on its website. The FAA declined further comment on Friday.

Local 591 raised the charges in a lawsuit against American last month.

American did not immediately respond for comment Friday. Executive vice president Stephen Johnson said last month that the lawsuit was frivolous and an attempt to get media attention and boost the standing of the union group's president.