In the case of Carey v. Brown, 1979, the U.S Supreme Court ruled that an Illinois statute prohibiting picketing in residential areas was unconstitutional because it violated the First Amendment's guarantee of freedom of speech. The law had allowed exceptions for labor disputes, which led to a challenge by non-labor protesters who were barred from demonstrating outside homes. The court held that this selective prohibition constituted content-based discrimination and thus infringed upon free speech rights protected under the Constitution. It further stated that while states have legitimate interests in protecting residential privacy and tranquility, these cannot be pursued through means that suppress or favor particular viewpoints.

In the dissenting opinion for Carey v. Brown, Justice Rehnquist disagreed with the majority's view that Illinois' labor picketing exception violated the Equal Protection Clause of the Fourteenth Amendment. He argued that this case was not about content-based discrimination but rather a distinction between public issue picketing and labor dispute picketing. According to him, these two types of picketing are fundamentally different in nature and purpose; hence they can be treated differently under law without violating constitutional principles. He also pointed out that there is no evidence showing Illinois had intended to suppress certain ideas or viewpoints through its regulation on non-labor related protests, which would have been unconstitutional. Instead, he believed it was within state’s power to regulate activities potentially causing social harm or disturbance such as residential pickets while allowing exceptions for historically recognized rights like labor disputes.