A government watchdog is calling for stronger oversight of air safety in response to a series of disclosures by air traffic controllers and other Federal Aviation Administration whistleblowers.

Special Counsel Carolyn Lerner, whose job is to protect from retaliation government employees who expose mismanagement or wrongdoing, sent letters Tuesday to the White House and Congress detailing a series of "troubling" FAA whistleblower cases.

Lerner said in a statement that FAA has one of the highest rates of whistleblower filings per employee of any government agency.

The counsel's office has received 178 whistleblower disclosures from FAA employees since 2007 — 89 of which related to aviation safety. Forty-four cases were referred to the Transportation Department for investigation, and all but five were substantiated.