The U.S. Supreme Court case Illinois State Board of Elections v. Socialist Workers Party et al., 1978, revolved around the constitutionality of an Illinois law that required new political parties and independent candidates to gather a certain number of signatures in order to appear on election ballots. The Socialist Workers Party argued that this requirement violated their First Amendment rights by making it excessively difficult for them to participate in elections. The court ruled in favor of the Socialist Workers Party, finding that while states have a legitimate interest in regulating elections, they must do so in a manner that does not infrive upon constitutional rights such as freedom of speech and association. Therefore, the signature requirement was deemed unconstitutional because it placed an undue burden on smaller political parties and independent candidates.

In the dissenting opinion for Illinois State Board of Elections v. Socialist Workers Party, Justice Rehnquist disagreed with the majority's view that Illinois' signature requirement violated the First and Fourteenth Amendments. He argued that states have a legitimate interest in ensuring that political parties demonstrate a significant modicum of support before they are placed on an election ballot to avoid voter confusion and frivolous candidacies. Furthermore, he contended that it is not unreasonable for states to require more signatures from new or small political parties than established ones because these groups have not yet demonstrated substantial public support. The justice also criticized the majority's reliance on statistical data as evidence of discrimination against minor parties, stating this approach was inappropriate in constitutional adjudication.