The White House has condemned a decision by the United States Supreme Court to remove the limit on how much companies can spend on political campaigns.
US President Barack Obama says the court has "given a green light to a new stampede of special-interest money in our politics.
"It's a major victory for big oil, Wall Street banks, health insurance companies and the other powerful interests that marshal their power every day in Washington to drown out the voices of everyday Americans."
Mr Obama pledged to work with Congress for a "forceful response".
The court's 5-4 vote ends a 20-year ban on businesses and unions using money from their own funds to pay for campaign ads, the BBC reports.
One of the court's nine judges, Anthony Kennedy, said the ban was a form of censorship.
"We find no basis for the proposition that, in the context of political speech, the government may impose restrictions on certain disfavoured speakers," he wrote.
Four liberals oppose ruling
His view was mirrored by that of Chief Justice John Roberts, who said that upholding the limits on corporate campaign spending would have restrained the "vibrant public discourse that is the foundation of our democracy".
But fellow judge John Paul Stevens disagreed strongly, saying that the court's ruling threatened to "undermine the integrity of elected institutions around the nation".
He was joined in his opposition to the ruling by the court's three other liberals, including Sonia Sotomayor, who was appointed by President Obama.
The court ruled that any campaign adverts not paid for by the candidate or their party must be clearly marked with the name of the sponsor.