PHILADELPHIA - Federal authorities on Thursday charged 37 current or former Boeing employees with selling or trying to buy illegal painkillers and anti-anxiety drugs at a suburban Philadelphia plant that makes military aircraft.

Following a four-year investigation, U.S. Attorney Zane David Memeger said 23 people were charged with selling the prescription painkiller Oxycontin and other illegal drugs and 14 were charged with attempted possession of various drugs.

All but one of those charged is a current or former Boeing Co employee. Another person was expected to be arrested.

"This investigation and prosecution focused not only on the sellers, but also on the users because of the critical role that these employees play in manufacturing military aircraft," Memeger told a news conference.

Boeing employs more than 6,000 people at the Ridley Park plant, where the V-22 Osprey vertical take-off aircraft and H-47 Chinook helicopters are produced.

There was no evidence that the integrity of the work on any aircraft had been compromised, Memeger said.

FBI and Drug Enforcement Administration agents launched the bust early Thursday morning at the plant.

Boeing spokesman Damien Mills said that in May 2006 some employees contacted the company's internal ethics group with suspicions there was illegal drug activity at the plant.

He said Boeing launched an internal probe, and in August 2007 turned its findings over to federal investigators.

Boeing issued a statement saying it "commends the U.S. Attorney's Office, and other federal law enforcement agencies for their rigorous and thorough investigation, throughout which we took appropriate steps to ensure safety of our employees and the absolute integrity and quality of the products we produce for our customers."

If convicted, those charged with distribution face possible sentences of 10 to 260 years in prison and millions of dollars in fines, the U.S. Attorney's office said.