The head of the Chicago police officers union on Tuesday called on its members to refuse to comply with the city’s COVID-19 vaccine mandate, which is set to take effect on Friday.

“Do not fill out the portal information,” Chicago Fraternal Order of Police President John Catanzara said in a video to officers posted on YouTube. “I’ve made my status very clear as far as the vaccine, but I do not believe the city has the authority to mandate that to anybody—let alone that information about your medical history.”

According to Catanzara, the police union is preparing a lawsuit against the city if Mayor Lori Lightfoot’s administration attempts to enforce the mandate, which requires city workers to report their vaccine status by Friday or be placed on a “no-pay” status.