The court has now ruled the measures unconstitutional, potentially unleashing more than $1 trillion a year in corporate money for political advertising in all forms. By comparison, Obama, McCain and the political parties spent $1.5 billion combined in the 2008 election; the most expensive in history.
"Ignoring important principles of judicial restraint and respect for precedent, the court has given corporate money a breathtaking new role in federal campaigns," Feingold said in a statement. "The American people will pay dearly for this decision when, more than ever, their voices are drowned out by corporate spending in our federal elections."
McCain also expressed disappointment with the ruling but insisted that some of the reforms imposed in 2002 still hold.
"It appears that key aspects of the Bipartisan Campaign Reform Act, including the ban on soft money contributions, remain intact," McCain said in a statement.
The soft-money ban regulates the financial contributions corporations and unions can make directly to political parties or candidates.
House Speaker Nancy Pelosi, D-Calif., said the Court's action "strengthens the hand of special interests in elections" and that her staff is closely examining the ruling.
But Republican National Committee chairman Michael Steele praised the Court's action, calling it an affirmation of Americans' constitutional rights. "We need to encourage a vibrant debate on the issues and not restrict the free exchange of ideas," he said.
Today's ruling is directly a victory for Citizens United, the conservative non-profit advocacy group that brought the suit, which had argued that the government was attempting to suppress corporate political speech.
The group produced in 2008 "Hillary: The Movie," a critique of then presidential candidate Hillary Rodham Clinton. The group decided to distribute its movie through a "video on demand" service accessible to cable subscribers.
The Federal Election Commission banned the release, ruling that the movie was a so-called "electioneering communication" -- comparable to an ad attacking a candidate -- and because it had been made with corporate funds was subject to restrictions imposed under the 2002 McCain-Feingold campaign finance law.
Citizens United sued arguing that its movie was not an "electioneering communication," and the case was initially heard last spring by the high court. But in late June, instead of an opinion, the justices issued a stunning order:
The court wanted to re-hear the case and directed parties to brief on a much broader issue: whether two court precedents dealing with the regulation of corporate spending -- Austin v. Michigan Chamber of Commerce and parts of McConnell v. FEC -- should be overturned.
The court held hearings in the case a month before the 2009 term officially began.
Lawyers for Citizens United argued that the government was attempting to suppress corporate political speech. Olson, a former solicitor general, arguing on behalf of the group, said, "Robust debate about candidates for elective office is the most fundamental value protected by the First Amendment's guarantee of free speech."
Elena Kagan, Obama's solicitor general, made her debut argument in the case, urging the court to avoid striking down campaign finance regulation but instead rule more narrowly.