Citizens United v. FEC (2010) held that the First Amendment protects independent political expenditures by corporations, unions, and other associations. SpeechNow.org v. FEC (2010), decided shortly after, allowed unlimited contributions to PACs that make only independent expenditures — creating the modern Super PAC.
The decision did not change limits on direct contributions to candidates or parties, nor did it overturn disclosure requirements. But subsequent IRS rules and tax-status regimes (501(c)(4) "social welfare" organizations) created channels for "dark money" — political spending whose donors are not publicly disclosed.
Reform proposals range from a constitutional amendment to overturn the decision, to disclosure-focused legislation (DISCLOSE Act), to public financing of campaigns.