Janet Jackson's Super Bowl performance sparked a decency row

A Parents Television Council review claimed many shows did not have enough prior warnings on sex and violence.

The group's president Brent Bozell said the ratings, which the TV networks support, had become "meaningless".

Congress is considering raising decency breach fines on channels to $500,000 (�263,000) and placing new rules on cable and satellite TV.

After monitoring 528 hours of 638 prime-time shows aired over six weeks, the group claimed many shows did not give accurate warnings.

Warning system

The review alleged that none of the 118 shows viewed on the NBC network had content warnings.

The group also claimed a large share of the ABC network's output failed to use accurate content labels.

Broadcasters are supposed to feature a letter sign prominently to indicate content - an "L" for bad language, "S" for sex and "V" for violence.

Broadcasters and cable companies developed the rating system for TV shows in 1996 following complaints.

'Over-reaching'

Most TV sets made after 1999 include a V-chip technology that allow parents to block shows based on ratings.

The PTC review was released on the eve of the annual meeting of TV and radio broadcasters, who plan to discuss the crackdown on content.

Television networks have supported ratings on their shows but have said regulators were over-reaching.