The US TV watchdog has defended its decision to fine 20 TV stations $550,000 (£281,000) for airing a flash of Janet Jackson's breast.
Around 90 million viewers saw Jackson's exposed breast
The Federal Communications Commission rejected arguments by the CBS network that her performance during the 2004 Super Bowl did not break decency rules.
It "violated longstanding prohibitions on indecent material", it said in a statement filed to an appeal court.
CBS is challenging the commission's ruling in the Philadelphia court.
Fellow singer Justin Timberlake ripped off part of Jackson's bustier, exposing her breast for less than a second during the half time performance at American football's showpiece event at the Reliant Stadium in Houston, Texas.
The network - which has paid the fine on behalf of the stations - said it was unaware the incident was going to happen.
CBS says the commission has not previously taken action against fleeting instances of nudity and profanity.
But the FCC dismissed this in its brief to the 3rd US Circuit Court of Appeals.
It said: "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."
Timberlake said the incident was down to a "wardrobe malfunction"
The agency also denied the standards by which it measures such incidents were subjective, another one of CBS's arguments.
US TV and radio stations are barred from airing "indecent" material between 0600 and 2200. The restrictions do not apply to cable or satellite stations.
Since the Super Bowl incident, American broadcasters have been under increasing pressure to clean up the airwaves.
In June, President George Bush signed a law increasing the maximum fine for airing unsuitable material to $325,000 (£174,000) for each station. Each of the 20 CBS stations which broadcast the Jackson incident had been fined $27,500.
This year the Rolling Stones were censored during their Super Bowl half-time slot after some lyrics were deemed sexually explicit.
Prince is due to perform at 2007's Super Bowl final, on 4 February at the Dolphin Stadium, near Miami.