Federal authorities have charged Democratic Congresswoman LaMonica McIver with two counts of assault after a confrontation with officers outside an immigration detention centre.
Alina Habba – the interim US attorney for the state and a former personal attorney to President Donald Trump – initially announced the charges in a social media post late on Monday.
Habba also said that her office would drop a trespassing case against the mayor of Newark, Ras Baraka, who is also a Democrat.
Scuffles broke out when McIver, Baraka and others paid an oversight visit to the Immigration and Customs Enforcement (Ice) centre in Newark on 9 May. No injuries were reported.
The Democratic lawmakers were visiting Delaney Hall, which can hold up to 1,000 people and was touted by the Department of Homeland Security (DHS) as the first reopened immigration facility under the new Trump administration.
Videos showed increasingly heated discussion and a chaotic scene including police, Ice agents, journalists, the politicians and protesters before Mayor Baraka was arrested.
The formal complaint, unsealed on Tuesday, alleges that McIver pushed Ice agents with her forearms and joined in efforts to prevent them from arresting Mayor Baraka.
The eight-page document includes several screenshots from cameras worn by Ice officers that show McIver, in a bright red jacket, inside a crowd of politicians and law enforcement.
She is charged with two counts of assaulting, resisting, and impeding certain officers or employees.
Federal law prohibits immigration officials from blocking access to detention facilities for members of Congress seeking to conduct oversight, and grants lawmakers and designated staffers special access.
The members of Congress present on 9 May were eventually granted access and given a tour of the building.
It is unusual for US attorneys to charge sitting members of Congress, though not unprecedented.
Individual lawmakers have in the past faced charges on fraud, bribery, and campaign finance violations.
Members of Congress are occasionally arrested at protests, but those incidents are primarily symbolic and rarely lead to criminal charges.
Charging a member of Congress requires consultation or approval Department of Justice’s public integrity section in Washington DC.
That oversight exists to “avoid compromising the credibility and the public perception of the justice department, and how especially political or politically sensitive prosecutions are handled”, said John Keller.
Mr Keller resigned from the unit in February after the department moved to drop the corruption case against New York City Mayor Eric Adams – one of several high profile departures since Trump took office.
The Department of Justice did not immediately respond to a BBC inquiry about whether the protocols set out by the agency had come into play in McIver’s case.
Matt Platkin, the New Jersey attorney general and the state’s highest-ranking law enforcement official, called the charges against McIver “an extraordinary step that requires clear evidence of criminal conduct and intent”.
Administration officials and the Democratic lawmakers opposed to the Ice facility each blamed each other for the incident.
Commenting on the case, Trump told reporters that McIver had been “out of control”, and DHS said the politicians “stormed the gate and broke into the detention facility.”
Tom Homan, the administration’s border czar, told reporters that there was a “right way and a wrong way” for lawmakers to check on the state of detention facilities.
McIver has denied wrongdoing and maintained she was “fulfilling our lawful oversight responsibilities.”
She called the case against her “purely political”, while leading congressional Democrats issued a statement saying the charge of assaulting, impeding or interfering with law enforcement “is extreme, morally bankrupt and lacks any basis in law or fact”.
Baraka said the videos taken during the incident “make it clear that Delaney Hall personnel opened the gate for me, and allowed me to enter the property, as well as my calm and respectful departure when asked to leave”.
In dropping the charge against the mayor, Habba, who went on to serve as a spokeswoman for Trump before he named her the top federal prosecutor in New Jersey, said she would personally give Baraka a tour of the facility.