Last year, the American Freedom Defense Initiative (AFDI) wanted to run anti-Islam ads on SEPTA, Philadelphia's transit system. The controversial ads depict a photo of Adolf Hitler talking to a Palestinian leader. The words underneath: "Islamic Jew-hatred. It's in the Quran."

SEPTA, like other transit agencies, tried to reject the ads, but was taken to court — and lost. So in October, SEPTA redefined its ad space. Instead of being a public forum, its ad space would now be a limited public forum. Under those rules, it said it can ban political speech. Seattle's transit agency took the same action. 

Ruthann Robson, a law professor at the City University of New York, said it’s not that different from banning cigarette ads, which was what New York City did in 1992.

"The advertising on buses was never a totally open forum, right?" she said. "One: you had to pay for the advertising, and two: you could reject ads."

The AFDI has also bedeviled New York. And, like SEPTA, the MTA has tried to block the ads, but lost in court — most recently, over an ad quoting Islamic extremists praising the killing of Jews. So this week, the MTA took a page out of SEPTA’s playbook and voted to redefine its ad space as a limited public forum.  

But noted First Amendment attorney Floyd Abrams said the MTA is on shaky legal ground.

"I think they're on the wrong side of the First Amendment," he said, "and I don't think their effort to ban political ads while allowing commercial ones is going to pass muster. I think it's sort of an inversion of First Amendment principles."

One problem: The MTA agency will still run advertising touting plastic surgery, or slasher movies. It just won’t run ads that contain viewpoints.

"We're talking here about a city, a government agency," said Abrams, "making a decision that they want to be politics-free at the same time they are accepting commercial communications."

There is precedent for the MTA's and SEPTA's rejection of controversial ads. In 1970, a candidate running for state assembly in Ohio wanted to place advertisements inside Shaker Heights buses. The city's transit system refused, and the case went up to the Supreme Court. And in Lehman vs. City of Shaker Heights, the high court upheld the city's ban on political advertising on public transportation.

But that might not give the MTA legal cover.

Richard Briffault, a law professor with Columbia University's law school, said Shaker Heights had been consistent in always banning political ads on public transportation.

"In some ways," he said, "the question here is if the MTA allowed (political speech) in the past, and now they're narrowing it down, I'm not quite sure what rules would apply if they decide they want to redefine the scope of their public forum."

So the MTA's previous acceptance of political speech might hamper its ability to excise it now.

And the agency can expect its new policy to be challenged. Pamela Geller, the head of AFDI, said she plans to sue the MTA. Even if its new policy stands, Geller's ad could still get through, which is what happened in Philadelphia. A judge ruled that because Geller submitted her ads to SEPTA under the transit agency’s previous advertising policy, SEPTA had to accept them. They’re now adorning the outside of 84 buses — and are only scheduled to be taken down Friday.

One transit agency that still accepts political advertisements: D.C.'s Metro. "We have no plans to change our advertising guidelines," said spokeswoman Morgan Dye. "The courts have ruled that Metro advertising space is a public forum."