In Perry Ed. Assn. v. Perry Local Educators' Assn. (1983) 460 U.S. 37, a divided Supreme Court held that permitting access to teachers' mailboxes and interschool mail to an incumbent teachers union and denying access to a rival union did not amount to viewpoint discrimination, because government can impose reasonable regulations on speech, as long as the limitations are necessary to serve a compelling state interest, are narrowly drawn to achieve that end, and are not an effort to suppress expression merely because public officials oppose the speaker's view. (Perry Ed. Assn. v. Perry Local Educator's Assn., supra, 460 U.S. at pp. 45-46 103 S. Ct. at pp. 954-956.)