The U.S. Supreme Court case City of Chicago v. Jesus Morales et al., 1998, revolved around a city ordinance in Chicago that prohibited criminal street gang members from loitering in public places. The law allowed police officers to order any group of people standing idly in a public place to disperse if the officer believed at least one person was a gang member. If anyone disobeyed, they could be arrested and fined up to $500 or imprisoned for six months. Jesus Morales and others challenged this ordinance as unconstitutionally vague because it did not sufficiently define "loitering," leading to arbitrary enforcement by police officers based on their subjective judgment about who is or isn't part of a gang. In June 1999, the Supreme Court ruled (6-3) that the anti-loitering law was indeed too vague and therefore violated due process rights under the Fourteenth Amendment because citizens couldn’t reasonably understand what behavior would constitute an offense under this law.

In the dissenting opinion for City of Chicago v. Jesus Morales et al., Justice Stevens, joined by Justices Souter and Ginsburg, argued that the majority's decision to strike down a local ordinance as unconstitutionally vague was incorrect. The dissenters believed that the law, which prohibited loitering in public places with known gang members without apparent purpose, could be interpreted narrowly enough to avoid constitutional issues. They suggested that 'apparent purpose' should be understood as any lawful activity or conduct consistent with customary use of public spaces. This interpretation would exclude innocent activities such as standing around or aimlessly wandering from being considered illegal under this law. Furthermore, they contended that even if some applications of the statute might infringe upon constitutionally protected rights like freedom of association and movement, it did not justify invalidating it entirely since many legitimate applications existed too.