The Justice Department is investigating Minnesota officials, including Gov. Tim Walz and Minneapolis Mayor Jacob Frey under the theory they conspired to impede federal immigration agents through public statements they have made, a senior law enforcement official and a person familiar with the matter told NBC News.

Minneapolis has been the backdrop of intensifying protests since an ICE officer fatally shot Renee Nicole Good, a mother of three and a U.S. citizen, last week. Immigration enforcement arrived in Minneapolis weeks ago, but federal officers have flooded the city since Good’s shooting.

Both Walz and Frey have been at odds with federal officials who have argued the officer, Jonathan Ross, was justified in shooting Good. They have criticized the federal response and questioned why the FBI cut out local authorities from the probe into the Good shooting. CBS News first reported on the investigation.

Walz said in a statement Friday the investigation is purely political.

“Two days ago it was Elissa Slotkin. Last week it was Jerome Powell. Before that, Mark Kelly. Weaponizing the justice system and threatening political opponents is a dangerous, authoritarian tactic,” he said. “The only person not being investigated for the shooting of Renee Good is the federal agent who shot her,” he said.

Frey said in a statement in response to reports of the DOJ investigation that he “will not be intimidated.”

“This is an obvious attempt to intimidate me for standing up for Minneapolis, our local law enforcement, and our residents against the chaos and danger this Administration has brought to our streets,” he said.

He added, “Neither our city nor our country will succumb to this fear. We stand rock solid.”

The Justice Department declined to comment. The federal statute used in the investigation into Minnesota officials has been rarely used and has roots in the Civil War-era. But it was on a list of statutes listed in a memo from Attorney General Pam Bondi last month, obtained by NBC News, that offered a roadmap for federal prosecutors on how to boost investigations into individuals she dubbed domestic terrorists.

Bondi posted on X Friday, “A reminder to all those in Minnesota: No one is above the law.”

The prospect of an investigation which would involve political speech by public officials raises First Amendment concerns that normally would involve a consultation with the Justice Department’s Public Integrity Section before federal officials opened a criminal probe into public figures or took any proactive investigative steps, according to a person familiar with the matter.

But the Public Integrity Section has been decimated and sidelined in Trump’s second term.

Aaron Terry, director of public advocacy for the Foundation for Individual Rights in Education, said in a statement Friday that if criticism of the administration’s immigration enforcement operations is the basis for the investigation, “it is blatantly unconstitutional and intolerable in a free society.”

“The right to condemn government action without fear of government punishment is the foundation of the First Amendment,” Terry said.

In Minneapolis, tensions continue to run high; a federal officer shot a man in the leg in Minneapolis on Thursday night after he allegedly fled a traffic stop and attacked an officer.