The vote was along the court's ideological fault line, the same breakdown that decided Citizens United vs. FCC in January 2010. Citizens United opened the floodgates to corporate and union political donations.
When the U.S. Supreme Court stayed, or temporarily blocked, the state court decision in February, Justices Ruth Bader Ginsburg and Stephen Breyer suggested the high court should take the opportunity to take another look at Citizens United.
The challengers to the Montana law, a small group of non-profits and corporations, told the U.S. Supreme Court in their petition that the riot of independent spending following Citizens United is irrelevant.
The Supreme Court majority said there was little difference between the struck-down federal law and the Montana law.
"In Citizens United vs. Federal Election Commission, this court struck down a similar federal law, holding that 'political speech does not lose First Amendment protection simply because its source is a corporation ...,'" the Supreme Court majority said in a per curiam, or unsigned, opinion, Monday. "The question presented in this case is whether the holding of Citizens United applies to the Montana state law. There can be no serious doubt that it does."
Justice Stephen Breyer, joined by the court's three other liberals, dissented.