A federal judge in Minnesota quashed the Justice Department’s subpoenas of state and local officials in a ruling unsealed on Monday, finding that the Trump administration had engaged in a politically motivated and improper use of the grand jury process. Those subpoenas were issued at the height of the administration’s winter immigration crackdown in the state.

Chief Judge Patrick J. Schiltz wrote in a highly critical opinion that “the dominant purpose of the challenged subpoenas is to coerce Minnesota officials into assisting the federal government with enforcing civil immigration law and to harass and retaliate against them for failing to do so.”

Judge Schiltz, who was nominated to the bench by President George W. Bush, had previously raised concerns with the conduct of the Trump administration during Operation Metro Surge. That crackdown, which involved thousands of agents, led to thousands of arrests in Minnesota and three shootings in Minneapolis.

At one point this winter, Judge Schiltz ordered the leader of Immigration and Customs Enforcement to appear in his courtroom to explain why people arrested by immigration agents had been held without an opportunity to challenge their detentions. He later backed off that demand when an immigrant at the heart of the case was released.

A spokeswoman for the Department of Homeland Security referred to a previous order from Judge Schiltz as a “diatribe from this activist judge.” The department did not immediately respond to a request for comment on Monday.

The Justice Department said in a statement on Monday that it “takes the unlawful obstruction of federal law enforcement operations extremely seriously and will continue to act in full compliance with the law to investigate these matters.”

In January, at the height of what the Trump administration called Operation Metro Surge, the Justice Department subpoenaed the offices of several prominent Minnesota Democrats who were critical of the Trump administration’s immigration policies. The subpoenas sought records related to those offices’ policies on immigration enforcement.

Judge Schiltz wrote on Monday that the justification given for the subpoenas was an investigation into possible violations of federal laws that make it illegal to conceal an undocumented immigration or obstruct the government.

But in fact, the judge wrote, the “subpoenas are directed to investigating activity that is not only legal, but constitutionally protected from interference by the very federal government that issued the subpoenas.”

The officials whose offices received subpoenas included Gov. Tim Walz, Attorney General Keith Ellison, Mayor Jacob Frey of Minneapolis and Mayor Kaohly Her of St. Paul, several of whom issued statements on Monday praising the judge’s ruling as a victory for the rule of law.

“No one should be targeted for questioning those in power,” Mr. Frey said in a statement. “No community should be expected to accept harmful policies without objection. And no administration should use the tools of law enforcement to silence dissent.”