The U.S. Supreme Court case Nixon v. Shrink Missouri Government PAC in 1999 revolved around the issue of campaign finance limits and their constitutionality under the First Amendment's protection of free speech. The state of Missouri had imposed contribution limits to political campaigns, which were challenged by Shrink Missouri Government PAC as a violation of their freedom of speech rights. The court ruled in favor of Nixon, upholding that these limitations did not infrally upon First Amendment rights but rather served to combat corruption or its appearance within politics. This decision affirmed an earlier ruling (Buckley v Valeo) where it was held that restrictions on contributions do not limit political expression as much as expenditure limitations would.

In the dissenting opinion for Nixon v. Shrink Missouri Government PAC, Justice Clarence Thomas argued that campaign contribution limits infringe upon First Amendment rights to free speech and association. He contended that political contributions are a form of expression protected by the Constitution, and as such, should not be subject to government-imposed limitations unless there is compelling evidence of corruption or undue influence. In this case, he believed no such evidence existed. Furthermore, he criticized the majority's reliance on Buckley v. Valeo (1976), arguing its reasoning was flawed and inconsistent with original understanding of the First Amendment when it comes to campaign finance laws. He also expressed concern about potential chilling effects on political participation due to these restrictions.