Singer Janet Jackson performs with singer Justin Timberlake during the halftime show at Super Bowl XXXVIII in Houston, Texas, in this February 1, 2004 file photo. The Federal Communications Commission late on Friday defended its decision to fine 20 CBS Corp. television stations $550,000 for airing a brief breast flash by Jackson.

The Federal Communications Commission late on Friday defended its decision to fine 20 CBS Corp. television stations $550,000 for airing a brief breast flash by pop singer Janet Jackson.

The agency rejected CBS's argument that her performance during the live 2004 Super Bowl football halftime show did not violate decency standards that restrict nudity on broadcast television.

"The FCC reasonably concluded that, although brief, this display of nudity violated longstanding federal prohibitions on the broadcast of indecent material," it said in a brief filed with the U.S. Court of Appeals for the Third Circuit.

Fellow pop singer Justin Timberlake ripped off part of Jackson's bustier exposing her breast for less than a second during the show. Despite the brevity, lawmakers and regulators were outraged and vowed a crackdown on broadcast indecency.

"The commission also reasonably held that CBS's violation of its broadcast indecency rules was "willful" and therefore justified a forfeiture," the FCC said.

U.S. television and radio broadcasters are barred from airing obscene material and are limited from broadcasting indecent materials between the hours of 6 a.m. and 10 p.m., when children are likely to be watching. The restrictions do not apply to cable or satellite services.

CBS apologized and paid the fine, $27,500 for each of the 20 stations it owns, but said it was not clued in ahead of time about the stunt and in July appealed the decision to the court, based in Philadelphia.

The network challenged the FCC's ruling that the flash was indecent, contending that it was brief and that in the past the FCC had not taken action against fleeting instances of nudity and profanity.

"If CBS doubted the applicability of indecency regulation to brief nudity, its doubts should have been dispelled in the days before the Super Bowl when the commission found apparently indecent the broadcast of nudity lasting less than a second," the FCC said.

The agency denied that its contemporary community standards by which it measures such incidents was subjective, another argument by CBS.

A representative for CBS was not immediately available for comment.

The case is the second major legal challenge to the FCC's decency standards. Earlier this week, an appeals court in New York heard oral arguments about the fleeting use of profanity on broadcast television.