The mechanic, Donald Gene Buchanan, 64, was inspecting a Continental Airlines plane when he was sucked into a jet engine in 2006.
Some members of the Federal Administration team that granted immunity to the pilots had ties to Continental, The Dallas Morning News reported Thursday.
A veteran safety inspector, Phil Thrash, who objected to the amnesty, has been called to testify April 1 before the U.S. House Transportation and Infrastructure Committee.
The complaint signals a widening of an investigation led by Rep. Jim Oberstar, D-Minn., into recent problems with Southwest Airlines and other allegations in the FAA's Southwestern region.
The FAA said the Continental crew's mistakes weren't intentional and were dealt with by retraining and the issuance of a written warning.