(Reuters) - AMR Corp’s American Airlines faces an increasing dispute with Federal Aviation Administration (FAA) regulators over allegedly improper repairs to at least 16 aircraft, the Wall Street Journal said, citing people familiar with the matter.

The paper said FAA officials suspect one of those planes was abruptly retired to get it out of sight of government inspectors.

The probe, which began several months ago, has raised red flags at the FAA about the Fort Worth, Texas-based carrier’s willingness to properly disclose potential safety problems, the people told the paper.

According to the paper, the latest case is viewed as particularly serious because some FAA inspectors think the circumstances under which the airline suddenly chose to mothball one plane show the move was part of an effort to hide the extent of suspected defects.

The plane was ferried to the New Mexico desert in March for storage, the paper said, citing people familiar with the probe and company documents, which were reviewed by the Journal.

“The FAA has provided American the opportunity to respond to its investigation, and we are in the process of doing so.” American spokesman Tim Wagner told the paper, but declined to elaborate, adding “we believe conversations outside of that process are inconsistent with FAA regulations.”

The FAA and American Airlines could not be immediately reached for comment by Reuters out of regular U.S. business hours.