In the case of Perry Education Association v. Perry Local Educators' Association et al., 1982, the U.S Supreme Court ruled that a school district's policy allowing only one teachers union to use its internal mail system did not violate the First Amendment rights of other unions. The court held that while public facilities may be designated as open forums for expressive activity, they are not required to do so and can limit access based on reasonable criteria. In this instance, granting exclusive access to one union was seen as a permissible means of maintaining labor peace within the school district. Therefore, it was concluded that such exclusivity did not infrally upon free speech or equal protection rights under the Fourteenth Amendment.

In the dissenting opinion for Perry Education Association v. Perry Local Educators' Association, Justice Brennan argued that the majority's decision was a significant departure from established First Amendment jurisprudence. He contended that public school mailboxes should be considered a public forum as they had been used extensively by various organizations and individuals to disseminate information. Therefore, denying access to these mailboxes based on union affiliation constituted viewpoint discrimination which is prohibited under the First Amendment. Furthermore, he disagreed with the majority's assertion that allowing exclusive access to one union served a compelling state interest in maintaining labor peace; instead, he believed it could potentially exacerbate tensions between rival unions and undermine free speech rights of teachers who were not members of the favored union.