The Transportation Security Administration issued a confidential warning to air carriers on July 22. The warning did not cite any specific case but said the government "continues to receive" reports about thefts.
It adds that "recent reporting also suggests a possible trend in the thefts of uniforms, vehicles and other items used by police, firefighters and emergency response personnel."
One occurred last month at the New York home of two flight attendants for Delta Air Lines, the paper said.
The FBI investigated that case and another in Kansas City, Missouri, in which a delivery truck containing uniforms of airport workers was stolen. The truck was recovered but the uniforms were not.
Investigators said they found no link to terrorism in either incident, according to the Post, but they continue to keep tabs on both situations.
"The threat is very real," Capt. Stephen Luckey, head of security for the Air Line Pilots Association, a union representing some 67,000 commercial pilots, told the Post.
Luckey said the pattern of such incidents cannot be dismissed.
"Taken out of context, individually, I don't think they're that significant. But when you put them together they paint a fairly good mosaic of threat," he said. "In light of the 9/11 attacks . . . I think this is an actual indication of something that requires a little more than casual attention."
The government warning urged airport security officials to be vigilant about checking employee identification cards.
It also suggested a "possible trend" in the reported thefts of uniforms, vehicles and other items used by police, firefighters and emergency personnel, the Post said.
Terrorists have been known to impersonate authority figures in other countries, such as when Palestinian attackers dressed as Israeli soldiers and bombed a bus last month in Israel, the Post pointed out. Earlier this year, London's Heathrow Airport was robbed twice in five weeks by bandits wearing security uniforms.
Rumors about terrorists posing as law enforcement or rescue personnel abounded in the United States shortly after the Sept. 11 attacks, and as recently as June two Middle Eastern men were questioned by police after trying to buy a used ambulance in New Jersey.
The US Airways unit of the Association of Flight Attendants warned its members last month about the dangers of "identity theft" while traveling, offering tips on how to secure hotel rooms and advising members to make copies of IDs and other documents in case the originals are stolen, the newspaper reported.
Pilots and flight attendants say they increasingly feel they're being watched or even followed when traveling abroad, the Post added.
The Northwest Airlines unit of the pilots' union issued a security alert to its members on July 2, warning that "flight crews from other airlines have reported being the subjects of obvious surveillance by Mid-Eastern looking males and females" while traveling in Frankfurt, Amsterdam and London.
One American Airlines flight crew member who asked the Post not to be identified said a co-worker was in a London pub during a layover when "a Middle Eastern man started taking pictures" of her and other crew members.
"There are lots of stories of stalking, and I don't know of these kind of stories before 9/11," the American employee said.
The pilots' union is calling for the TSA to create a new airport badging system using a biometric component, such as iris scans or fingerprints, to verify the identity not only of pilots but also of any armed federal agents who may be on a flight.
Meanwhile, Luckey has sent pilots tips on counter-surveillance techniques, such as how to sneak a photo of a suspicious person. Stalking incidents, like thefts of uniforms, are "demonstrably a very viable threat and something we need to guard against," he said.