Denver has long banned certain uses and activities in its parks, including feeding wildlife, rock-climbing, and illegal drug use.

But starting this week, a city directive will also ban certain people from its parks. If the Denver police determine that a person has committed an illegal drug offense in a park, that person will be banned from all city parks for 90 days.

The new rule, which will be in effect for six months, is in response to the emergence of what Denver Parks and Recreation calls a “hub for drug sales and use” along the Cherry Creek Greenway, which runs through an otherwise well-off area southeast of downtown. The city says it has collected more than 2,400 needles from parks since April.

Naturally, the American Civil Liberties Union of Colorado says the ordinance is illegal. “The parks director has the authority to ban activities and has the authority to ban uses in the park,” Mark Silverstein, the legal director of the ACLU of Colorado, told the Denver Post. “The executive director does not have the authority to ban people.”

The directive makes no presumption of innocence and gives full power of suspension to the police. “The person subject to the Suspension Notice need not be charged, tried or convicted of any crime, infraction, or administrative citation in order for the Suspension Notice to be issued or effective,” it reads.

Denver’s order is actually a relatively modest version of more expansive “parks exclusion” laws that exist in Seattle; Portland, Oregon; and other cities. These laws allow police to ban residents from all city parks for a number of minor infractions, like having a dog off a leash. If they return to the park in violation of the ban, they can be arrested.

“Prior to the adoption of those laws, individuals could be removed from public parks only if there was probable cause that they had committed a criminal offense. More minor rule violations, such as being in the park after closing time, resulted only in a citation,” write Katherine Beckett and Steve Herbert in Banished. “Parks exclusion laws authorize police and parks officials to ban persons for committing minor infractions.”

Essentially, it’s a clever way cities can circumvent the unconstitutionality of vagrancy laws. Shortly after Seattle’s law was enacted, the ACLU reported that almost half of those banned from parks were “obviously” homeless. The majority of offenses were open container violations. I’d wager that very few residents have been banned from Seattle parks for not having a tow rope in proper condition stored on their boat.

In Denver, like in other cities, banned parkgoers can appeal. In practice, only a fraction of people do: The time frame to appeal is often limited to 10 days, and the banned don’t have a right to counsel.