Immigrants in Chicago and other U.S. cities have been preparing for immigration arrests since President-elect Donald Trump won the November election.

Immigrants and groups advocating for them have been preparing since Trump made mass deportations a signature pledge of his campaign. Trump has often been critical of Chicago, which has some of the country’s strongest protections for people in the country without legal status.

Details of planned immigration raids are unclear, but they would be the opening step in the president-elect’s goal of overseeing the largest deportation program in history.