Roth v. United States
In Roth v. United States, 34 U.S. 476 (1957), the U.S. Supreme Court held that there is no First Amendment protection for obscenity, and therefore States and municipalities can ban pornography. "We hold that obscenity is not within the area of constitutionally protected speech or press." Calling Roth "the first time the question has been squarely presented to this Court," the Court stated that "expressions found in numerous opinions indicate that this Court has always assumed that obscenity is not protected by the freedoms of speech and press."
The Court cited precedents in support of this ruling dating back as far as 1877.
The Warren Court essentially overruled this decision about a decade later in Memoirs v. Massachusetts.