By Ian Bush

PHILADELPHIA (CBS) – There are red light cameras at a couple dozen intersections in Philadelphia, but there’s one group that says it doesn’t have to pay if its drivers get a ticket.

The US Postal Service is in a spat with American Traffic Solutions, which manages many red light camera programs — including Philadelphia’s.  ATS says the USPS is ignoring violations its mail carriers are racking up.

“The local government is trying to go on the cheap to enforce traffic laws, and they’re trying to enlist the Postal Service. And the Postal Service is simply saying ‘no’,” says Dan Filler, a professor of law at Drexel University’s Earle Mack School of Law.

The USPS, in a letter to ATS from its Philadelphia-based senior litigation counsel, says it “enjoys federal immunity from state and local regulations.”

The response was met with scathing correspondence from the camera company, which said the USPS is “aiding and abetting your drivers in a blatant disregard for traffic laws.”

A speeding ticket is one thing — a cop would give that directly to a driver.  But the USPS tells KYW Newsradio that while its drivers must follow road rules, there’s no legal way to transfer an automated red light violation from a truck it owns to the unionized driver behind the wheel.

ATS spokesman Charles Territo doesn’t buy it.

“There’s a process in place already where the owner of a vehicle can share the liability with the individual driving the vehicle, as long as they identify who that individual was,” he says.  “We’ve advised the Postal Service that if they wish to transfer the liability, they have every right to do so.”

The right, perhaps.  But the USPS says it “cannot legally be billed for any traffic violation fines incurred by its employees” — so the tickets sit in limbo.

A spokeswoman for the Philadelphia Parking Authority says it hasn’t issued any red light tickets to postal trucks in the city.  Erin Gill, the deputy solicitor of Cherry Hill, says officials haven’t encountered any problems with USPS drivers and red light cameras (operated by Redflex) in the township, but “if we do receive any such violation in the future, we would absolutely issue it.”

But this has been a problem in East Cleveland, Ohio, according to Territo.

“The vehicle in question had received eight violations for everything from red light violations to speeding [captured by an automated speed device] in a school zone,” he says.

Territo says the checks never came in the mail.

Now, Tom Carper’s spokeswoman tells us the Delaware Senator and chairman of the Homeland Security and Governmental Affairs committee is looking into the matter.

“What they’re saying to the local police is if you want to pull over a truck and want to give that driver a ticket, go for it,” says Prof. Filler.  “But don’t ask us to go and research your thousands of electronic camera tickets.”

Filler says it’s what we should expect when aggressive, high-tech laws are adopted.

“If you give tickets to cars for traffic lights rather than to drivers, then sometimes you’re going to give a ticket to someone who doesn’t have a legal responsibility to pay it.”

The American Postal Workers Union, which represents postal employees, did not return repeated calls for comment.