Answer: Citizens United v. Federal Election Commission.
Step-by-step explanation:
In the Citizens United v. Federal Election Commission, 558 U.S. 310 (2010) case, the Bipartisan Campaign Reform Act that prohibited any investments in political campaigns by businesses and labor organizations, was a violation of the protection of free speech guaranteed by the First Amendment.
Before that, the Tillman Act of 1907 had been the first legislation to ban financial contribution from corporations to political campaigns.