WASHINGTON (CNN) - Indecent material broadcast on Howard Stern's radio show may cost six Clear Channel stations a total of $495,000, the Federal Communication Commission said Thursday, prompting the radio chain to drop Stern's show from six stations.

The FCC voted to fine Clear Channel the maximum amount of $27,500 for each of 18 violations.

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"Mr. Stern's show has created a great liability for us and other broadcasters who air it," said John Hogan, president and CEO of Clear Channel Radio, in a news release. "The Congress and the FCC are even beginning to look at revoking station licenses. That's a risk we're just not willing to take."

The Howard Stern show is known for sexually explicit and graphic discussions.

"Since I arrived at the commission, we have greatly stepped up our enforcement against indecent broadcasts," FCC Commissioner Jonathan Adelstein said. "I expect that stepped-up actions like those we take today will convince broadcasters that they cannot ignore their responsibility to serve the public interest and to avoid the broadcast of indecent material over the public airwaves."

The commission ruled the stations -- WBGG-FM in Fort Lauderdale, Fla.; WTKS-FM, Cocoa Beach, Fla.; WTFX-FM, Louisville, Ky.; KIOZ-FM, San Diego; WNVE-FM, Honeoye Falls, N.Y.; and WXDX-FM, Pittsburgh -- all knowingly and willfully broadcast indecent material played on the Stern show.

Clear Channel said in its release that it had "asked for assurances from the show's syndicator that steps would be taken to bring the program into compliance with FCC regulations," but "no such assurances were ever given."

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"We had hoped to return Mr. Stern's show to the air free from indecent content," Hogan said. "Unfortunately, the FCC's latest action, combined with deafening silence from the Stern show on their future plans to comply with the law, leave us no choice but to abandon the program for good."

Earlier this year, Clear Channel (CCU: Research, Estimates) said it was initiating a "responsible broadcasting initiative," that included a zero-tolerance policy for indecent content. It promised "strict disciplinary action for anyone that violates federal law or FCC regulations on the air."

Stern, in a statement posted on his Web site, said he was not surprised by Clear Channel's decision to drop his program and accused the FCC of conducting a "McCarthy-type witch hunt."

"It is pretty shocking that governmental interference into our rights and free speech takes place in the U.S.," Stern said. "It's hard to reconcile this with the 'land of the free' and the 'home of the brave.' "

A Viacom spokesman told CNN that Infinity Radio does not have any plans to cancel the Howard Stern show from its radio stations. The company says that currently Howard Stern is carried by 35 radio stations nation wide.

Viacom (VIA: Research, Estimates), the parent company of Infinity Radio, would not make any further comment on the matter.