Citizens United v. FEC came before the U.S. Supreme Court in 2009.
In 2008, lobbying group Citizens United was prevented from airing commercials for its political documentary, which was highly critical of then presidential-nominee Hillary Clinton. The group was found in violation of the Bipartisan Campaign Reform Act, which prohibits corporations and unions to broadcast advertisements mentioning a candidate within 30 days of a primary or 60 days of a general election.
The Court ruled the First Amendment prohibits the government from restricting campaign contributions by a non-profit. The ruling was later extended to include for-profit companies.