The law is named after its Senate champions John McCain and Russ Feingold

By a 5-4 vote, the court ruled that it was constitutional to ban unregulated contributions known as "soft money".

It also upheld restrictions on TV and radio "issue ads" by corporations and unions right before elections.

Congress approved the law and President George W Bush signed it in 2002, but a number of opponents challenged it.

The challengers included the Republican Party, the California Democratic Party, the AFL-CIO trades union federation, the National Rifle Association, the American Civil Liberties Union, and the Chamber of Commerce business group.

Large soft-money contributions to national political parties give rise to corruption Supreme Court ruling

Supporters of the McCain-Feingold law - named after its Senate sponsors - see it as necessary to close loopholes and protect the integrity of elections.

A majority on the nine-strong court - divided between liberals and conservatives - agreed with them.

"There is substantial evidence to support Congress' determination that large soft-money contributions to national political parties give rise to corruption," the ruling said.

Working overtime

Analysts say the decision is one of the most important in the court's current term.

It sets the rules under which candidates and parties will have to operate in next year's presidential and congressional elections.

The case reached the Supreme Court after a ruling by a lower court struck down nine provisions of the law in May .

Twelve appeals against the ruling had been filed with the Supreme Court.