Three former Boeing Co. (BA) employees have alleged that the top U.S. planemaker installed improperly fitting parts in hundreds of Boeing 737 commercial jets, the Washington Post reported on Monday.

Boeing has denied the whistle-blowers' claims, contained in a lawsuit filed in U.S. District Court in Wichita, Kansas, insisting that no faulty parts could have slipped past Boeing controls and that there is no safety issue related to the parts, the newspaper said.

Boeing officials could not immediately be reached for comment.

The parts at issue, manufactured by Boeing supplier AHF Ducommun of Los Angeles — a defendant in the lawsuit along with Boeing — were made between 1994 and 2002, the whistle-blowers said.

They claim that Boeing allowed thousands of parts to be installed on the planes even though the aerospace company knew they did not meet specifications. Boeing also retaliated against people who raised questions about the parts, the whistle-blowers claim.

The whistle-blowers initially made the claims in 2002, the newspaper said. A review by the U.S. Federal Aviation Administration and the Pentagon, which bought some of the planes, found the charges had no merit.

But the Washington Post said it had reviewed the FAA's probe and found that the agency failed to visit any airplanes to inspect the 200 types of parts questioned by the whistle-blowers.

Ducommun declined to comment on the allegations, beyond referring to the FAA's previous findings the allegations had no merit, the Post said.