Philadelphia has announced it will no longer detain undocumented immigrants for transfer to federal authorities without a court warrant. The move by Mayor Michael Nutter sharply cuts cooperation between Philadelphia police and U.S. Immigration and Customs Enforcement on holding detainees for potential deportation. Nutter signed the policy into law at a news conference on Wednesday.

Mayor Michael Nutter: “Every Philadelphian or person in Philadelphia has the right to feel safe, secure and protected. And I believe that our new policy, established by the executive order I will sign shortly, will promote safety, because residents and others who are here will not need to fear that interacting with their government will result in a detainer for themselves or their loved ones.”

Similar curbs have been enacted for two states and at least eight cities, but activists say Philadelphia’s effort may be the most progressive so far since it would effectively bring immigration holds to an end.