US broadcasters transmitting indecent material face a tenfold increase in maximum fines, to $325,000 (£175,000) per violation, under new legislation.
Jackson's "wardrobe malfunction" has gone down in TV history
President George Bush, signing the law, said the previous amount of $32,500 (£17,500) had been "meaningless".
"This law will ensure that broadcasters take seriously their duty to keep the public airwaves free of obscene, profane and indecent material."
The new bill does not change how unsuitable material is defined.
The FCC defines indecency as "language or material that, in context, depicts or describes, in terms patently offensive as measured by contemporary community standards for the broadcast medium, sexual or excretory organs or activities."
US broadcasters have been under pressure to clean up the airwaves since Janet Jackson's breast exposure during a dance routine at the 2004 Super Bowl.
Television network CBS was fined $550,000 (£297,000) for the "wardrobe malfunction".
That figure represented the total sum of fines for individual affiliated stations - each limited to $32,500.
In March this year, the Federal Communications Commission (FCC) proposed a record fine of $3.6m (£1.9m) for an episode of the missing persons drama Without A Trace.
The penalty, split between 111 affiliates of CBS, was later reduced to $3.3m (£1.8m).
Broadcasters are barred from airing indecent material between 6am and 10pm, although the restrictions do not apply to cable or satellite services.