The ACLU of Colorado demanded the Denver Parks Department stop enforcing a directive authorizing police to eject people suspected of illegal drug activity from city parks, saying it targets homeless people suspected of marijuana use.

The directive violates the Constitution by banning people without a hearing, conviction, or other due process, Mark Silverstein, director of Colorado ACLU, said in the letter sent Wednesday.

“Denver’s program of expelling persons from public parks is an end run around constitutional protections. Now that we have seen the program in operation, we also know that it has failed to target the dangerous and threatening behaviors that city officials cited to justify this drastic measure.”

The Parks Department initiated the temporary six-month program without an ordinance or vote of the City Council on Sept. 1, 2016.

In initiating the ban, Denver officials cited a “huge epidemic of heroin use” and associated violent behavior in the parks. But a review of the suspensions stemming from the directive shows that expulsions have primarily targeted homeless people who are suspected consumption or possession of marijuana, according to the ACLU.