The U.S. attorney general called out Boston Mayor Michelle Wu on social media Tuesday for the city's policy of not cooperating with federal immigration authorities.

A congresswoman says she plans to make criminal referrals to the U.S. Justice Department to investigate Boston Mayor Michelle Wu and three other mayors of so-called sanctuary cities. Why it matters: Boston leaders view the city's policy restricting police from helping with civil — not criminal — immigration enforcement as a stance welcoming people of all backgrounds and fostering trust between residents and police.

The theatrical hearing reflected enormous tensions as President Donald Trump continues a major crackdown on undocumented immigration, with Democrats and Republicans sparring over the course of proceedings.

Boston Mayor Michelle Wu is scheduled to testify before Congress on Wednesday alongside other Democratic mayors from major sanctuary cities. Those cities, which do not cooperate with U.S. Immigration and Customs Enforcement on civil immigration issues have been criticized for their refusal to help federal authorities,

Boston Mayor Michelle Wu went to the U.S. Capitol in Washington, D.C. for a hearing from the House Oversight Committee on so-called “sanctuary” laws in the cities of New York City, Chicago, Denver and Boston.