Which case established the precedent that political speech could be funded by unions and corporations?

The case that established the precedent that political speech could be funded by unions and corporations is Citizen's United v. Federal Elections Commission. This landmark decision, decided by the Supreme Court in 2010, ruled that corporations and unions have the same First Amendment rights as individuals with respect to political speech. The justices determined that restrictions on independent political expenditures by corporations and unions amounted to an infringement on the free speech rights guaranteed by the First Amendment.

As a result of this ruling, corporations and unions can spend unlimited funds on political campaigns and advocacy, enabling them to influence the political process significantly. This decision has had a profound impact on campaign finance laws in the United States, allowing for the rise of super PACs and increased financial involvement of organizations in elections. The ruling emphasized the importance of free speech, even when it involves spending money, thus shaping the landscape of political campaigning and expression in the country.