In the 2010 case Citizens United v. Federal Election Commission, the Supreme Court struck down sections of the Bipartisan Campaign Reform Act.
The law's "prohibition on corporate independent expenditures," Justice Anthony Kennedy wrote in the majority opinion, "is an outright ban on speech."
The case allowed for unlimited campaign spending by corporations, labor unions and similar organizations in elections.
Today, the Court hears McCutcheon v. Federal Election Commission, a case that challenges individuals' biennial spending limits on contributions to federal candidates.
As Michael Kang, professor at Emory University Law School, explains, if the Court rules for McCutheon, the case would overturn Buckley v. Valeo, the 1976 case decided in the wake of the Watergate scandal, in which the Court ruled that individual campaign spending limits did not violate the First Amendment.