New Delhi, Aug. 14 -- MINNEAPOLIS - In late January, a woman arrived at a meeting of anti-ICE activists held at a church in the Minneapolis suburb of Roseville. She spoke with neighbors and organizers, left when the session ended, and drove home. What she did not know was that a federal agent had photographed her car in the parking lot, run the license plate number, and assembled a government dossier recording her name, home address, employment, and family.

She was one of dozens quietly catalogued under what court filings, unsealed Thursday, describe as a sweeping covert surveillance program run by the Department of Homeland Security against the protest movement that arose in Minnesota after immigration agents killed two people in the Tw...