Turner v. Safley
In Turner v. Safley, 482 U.S. 78, 89 (1987), the U.S. Supreme Court upheld prison regulations against correspondence with other inmates but struck down a prison prohibition on marrying other inmates. Justice Sandra Day O'Connor wrote the opinion, which overruled a prior decision of the Court.
The Court held that prison rules restricting a prisoner's constitutional rights must be "reasonably related to legitimate penological interests." Id. at 89.