PHILADELPHIA (AP) — An atheist group is suing a Pennsylvania transit system over its refusal to run ads with the word “atheists” on the sides of buses.

The County of Lackawanna Transit System repeatedly rejected the ads sought by the Northeastern Pennsylvania Freethought Society, telling the group it doesn’t permit advertising space to be used as a forum for public debate. The transit system also told the group its ad might offend riders and hurt revenue.

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The atheist group filed suit Tuesday in federal court in Scranton. The suit says COLTS allowed many religious groups to advertise before the Freethought Society tried placing its ad in 2012.

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The group wants a judge to force COLTS to run the “atheists” ad.

The transit system’s lawyer is reviewing the suit. He’s expected to comment later.

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