The American Civil Liberties Union of Colorado sent a letter to the Denver Sheriff Department’s director of corrections Wednesday afternoon accusing the city of mistreating the 106 protesters arrested Monday evening.

“The initial information we have gathered raises serious questions regarding whether there were systemic and pervasive violations of the constitutional and statutory rights of those detainees, and their rights under international law,” ACLU staff attorney Taylor Pendergrass wrote to William Lovingier.

City officials were not immediately available for comment, though Capt. Frank Gale of the sheriff’s department said Tuesday that the arrested protesters were processed quickly and treated well.

Denver police arrested the protesters near Civic Center Park, using some pepper spray in the process. Police say protesters refused to disperse and were carrying rocks; protesters contend that officers needlessly harassed and arrested them.

All were transported to a temporary processing facility set up on the western outskirts of Denver and put in holding cells surrounded by chain-link fence.

ACLU officials say the protesters were mistreated in a variety of ways. Among them: The warehouse was kept too cold, vegetarians were denied food, and people were forced to go to the bathroom while handcuffed to others.

But chief among their complaints are that arrestees were not allowed to meet in private with attorneys and were thus misinformed about their charges and their rights. The group wants the sheriff’s department to immediately set up a space for attorneys to meet with future arrestees.

Furthermore, Pendergrass writes that police gave each arrested protester a form that included an incorrect list of charges. Officials forgot to cross out the ones that didn’t apply to each person and didn’t inform them until later, according to the letter. The letter also says officials wouldn’t let some people make calls until they decided whether to post bond or not.

All of these conditions together “call into question whether any guilty plea could have possibly been knowing or voluntary,” Pendergrass writes. “After spending hours sitting on the road, arrestees were transported to TAPS [Temporary Arrestee Processing Site] where they sat in ice-cold pens for hours without blankets, unable to sleep, unable to use the bathroom except with another person, some unable to make any phone calls.”