The Tillman Act, passed by Congress over 100 years ago, banned corporate contributions to federal political campaigns.
It is named after its progenitor and chief advocate, Senator Benjamin Ryan "Pitchfork Ben" Tillman,"one of the most despicable men ever to serve in the U.S. Senate and a man who, it can fairly be said, did more to put in place the Jim Crow system in the South than any other single person."
Read this interesting post on the Center for Competitive Politics website arguing that the genesis for campaign finance laws isn't to control corruption, but really is because its advocates agree with Tillman's famous quote, "I have come to doubt that the masses of the people have sense enough to govern themselves." and other elitist and powermongering reasons.
Campaign finance laws are to keep the powerful in power, and the powerless without power.