Originally Posted by Taylor
The Bipartisan Campaign Reform Act of 2002 (known as BCRA or McCain–Feingold Act)—specifically §203, which modified the Federal Election Campaign Act of 1971, 2 U.S.C. § 441b—prohibited corporations and unions from using their general treasury to fund "electioneering communications" (broadcast advertisements mentioning a candidate) within 30 days before a primary or 60 days before a general election.
A 501(c)(4) could not take a donation and put it in the independant expenditure account unless the donor specifically requested it. If they requested it, then their donation would have to be disclosed.
The Citizens United decision did not disturb prohibitions on corporate contributions to candidates, and it did not address whether the government could regulate contributions to groups that make independent expenditures. The Citizens United ruling did however remove the previous ban on corporations and organizations using their treasury funds for direct advocacy. These groups were freed to expressly endorse or call to vote for or against specific candidates, actions that were previously prohibited.
Before Citizens United: Donors could anonymously donate to a 501(c)(4)s general fund, but general funds couldn't be used for campaign adds. Donors could however publicly donate to a 501(c)(4)'s SSF or Independent expenditure fund.. and these are the only funds which a 501(c)(4) could use to run adds.
After Citizens United, Donors could anonymously donate to a 501(c)(4)s general fund, and that general fund could now be used to run adds.
Citizens' united didn't change the type of things a 501(c)(4), business, or union, could do. It changed how they were allowed to pay for it.
This ruling was frequently interpreted as permitting corporations and unions to donate to political campaigns, or else removing limits on how much a donor can contribute to a campaign. However, these claims are incorrect, as the ruling did not affect the 1907 Tillman Act's ban on corporate campaign donations (as the Court noted explicitly in its decision), nor the prohibition on foreign corporate donations to American campaigns, nor did it concern campaign contribution limits.