Federal immigration authorities began a large-scale enforcement operation in New York City on Monday, marking the start of a crackdown that officials say will focus on individuals who were released from local custody despite being the subject of ICE detainers.

According to sources, the operation initially launched in Queens and is expected to expand throughout the five boroughs and surrounding metropolitan area beginning Tuesday. The effort is being carried out by officers assigned to ICE’s New York field office, with no additional agents brought in from other parts of the country.

The operation follows weeks of warnings from White House Border Czar Tom Homan, who has repeatedly vowed to increase immigration enforcement in New York City. Homan has sharply criticized New York’s sanctuary-style policies, arguing they force ICE agents to locate and arrest individuals in the community after local jails decline to honor federal immigration detainer requests.

Last week, Homan said additional ICE resources would be directed to the city after an alleged attack on a federal building, though he stressed that the enforcement initiative had already been planned before that incident.

Officials said ICE is primarily targeting individuals with outstanding immigration detainers who were released from city or state custody instead of being transferred to federal authorities. Agents also expect to make so-called “collateral arrests” of other individuals found to be in the country illegally during enforcement actions, even if they were not the original targets.

New York’s Protect Our Courts Act prohibits federal immigration agents from making civil immigration arrests of people entering or leaving state courthouses, limiting one of ICE’s traditional enforcement locations. Despite those restrictions, Homan has maintained that anyone in the United States illegally is subject to immigration enforcement under federal law.