In Perry Ed. Assn. v. Perry Local Ed. Assn. (1983) 460 U.S. 37, a school district entered into a collective bargaining agreement that gave the teachers' union access to the district's interschool mail system and teacher mailboxes while denying such access to any other school employee organization. (Id. at p. 40.) No statute, ordinance, or regulation was at issue; there simply was a policy decision that was reflected in the collective bargaining agreement. After concluding that the internal mail system and teacher mailboxes were not public forums, the court upheld the exclusion as reasonable. (Id. at pp. 48-52.)