PHILADELPHIA (CBS) — The American Civil Liberties Union is suing SEPTA for allegedly banning ads about housing discrimination.

The ACLU says SEPTA banned an ad from The Center for Investigative Reporting that would have featured a graphic showcasing public data about racial disparities in the conventional home mortgage market in 61 metro areas across the U.S., including Philadelphia.

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SEPTA said it refused to run the proposed ad on its buses and trains because policy prohibits ads with “political” content and that the ads took a position on “matters of public debate.”

The ACLU says in the lawsuit that SEPTA’s advertising standards violate the First Amendment’s free speech clause.

“It’s always a bad idea to give the government the power to choose what ideas can be heard,” said Reggie Shuford, executive director of the ACLU of Pennsylvania. “Time and time again, the Supreme Court has rejected the notion that the government has a legitimate interest in censoring political speech or it finds offensive.”

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Shuford continued, “Debate on public issues is the cornerstone of participatory democracy. No government entity, including SEPTA, should single it out for censorship.”

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SEPTA says it will “vigorously defend against this lawsuit.”

“The Center for Investigative Reporting mistakenly claims that SEPTA violated its First Amendment rights by rejecting its proposed advertisement expressing a viewpoint on a matter of public debate. SEPTA’s decision is consistent with its advertising policy, which is constitutionally sound and necessary to ensure that our vehicles and stations do not become forums for political debate – and distract from our core mission of providing safe and reliable public transportation in an environment that is welcoming to customers and employees,” SEPTA said in a statement.

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The lawsuit was filed in the United States District Court for the Eastern District of Pennsylvania.