Reform advocates won a major victory at the U.S. Supreme Court Wednesday when the high court upheld the most important parts of a campaign finance reform law passed by the Congress last year.

By a 5-4 decision, the Supreme Court upheld the key provisions of a law that supporters say will curb the influence of money in U.S. politics.

The law was passed by Congress and signed into law by President Bush in 2002. It represents the most sweeping overhaul of campaign finance laws since those enacted in the wake of the Watergate scandal in the 1970s.

The Supreme Court upheld two main provisions of the campaign reform law. It said the government could ban so-called soft or unregulated money donations to political parties from corporations, unions and wealthy individuals. Those types of donations, which are separate from tightly regulated hard money donations to specific candidates, have totaled hundreds of millions of dollars in recent elections.

The high court also upheld restrictions on the type of political advertising candidates and political parties can use in the final stages of a campaign.

Reform advocates were ecstatic over the ruling. Fred Werthheimer is president of Democracy 21, a private group that has long fought to tighten campaign finance laws. "This is an historic decision," he said. "It is a huge victory in the battle to control the undue influence of money in American politics and to protect our democracy against corruption and the appearance of corruption."

Opponents of the campaign finance law argue that the restrictions on fundraising and campaign advertising amount to a violation of the U.S. Constitution's guarantees of free speech. They contend citizens should be able to contribute as much money as they want to either candidates or political parties.

James Bopp is with the James Madison Center for Free Speech. He says the court decision to uphold the campaign finance law gives congressional incumbents from both major political parties a huge advantage in campaign fundraising.

"They have accomplished that now, in a 5-4 vote of the Supreme Court, ripping the heart out of the First Amendment [which guarantees free speech]," he said.

But even some of the Supreme Court justices acknowledge this may not be the last word on the issue of campaign finance reform. Justice Sandra Day O'Connor helped write the majority opinion upholding the law. But her opinion included the caution that, "money, like water, will always find an outlet" in politics.