WASHINGTON- Twenty CBS-owned TV stations have challenged plans by federal regulators to fine them $550,000 collectively for airing Janet Jackson’s breast-baring Super Bowl performance.

The Federal Communications Commission in September said it planned to fine each of the stations the maximum $27,500 for violating broadcast indecency standards through their live February 1 telecast of Jackson’s notorious halftime show.

The singer’s brief flash of nudity during one of the year’s highest-rated television programs sparked outrage from family groups and lawmakers on Capitol Hill, an FCC investigation and an industry-wide backlash against sexually explicit TV and radio content.

While acknowledging the incident had become “a defining moment” in the commission’s aggressive campaign to combat indecency, the stations denied the fleeting glimpse of a woman’s breast violated decency standards.

The stations, owned by Viacom, argued the FCC wrongly concluded the performance was designed to “pander, titillate, and shock” viewers and said the proposed fine would violate their free-speech rights.

“Something cannot be ‘designed’ without advance knowledge,” the stations said in their reply to the FCC. Viacom and CBS have said they knew nothing in advance about plans by Jackson and her duet partner, Justin Timberlake, to rip open her costume and expose her breast.

“If it stands, the (proposed fine) will lead to the end of live broadcasting as we know it by placing broadcasters on notice that they risk massive liability and perhaps license revocation if they fail to adopt technical measures to avoid the possibility of a spontaneous transgression,” they said.

The agency received about 542,000 complaints about the halftime show, produced in part by Viacom’s MTV network. The FCC decided against fining the other 200-plus CBS affiliates that aired the show and are not owned by Viacom.

The FCC has been cracking down on broadcast radio and television stations for explicit sexual discussions and other incidents that are aired when children are likely to be watching or listening.

The $550,000 proposed fine for “an unplanned, fleeting exposure of a woman’s breast is anything but a ‘restrained’ or ‘cautious’ approach to enforcement,” the stations said.

An FCC spokesman was not immediately available for comment. The agency was unanimous in seeking the fine but some on the commission felt all the CBS stations that aired the incident should have been taken to task.