A federal judge agreed to quash the US federal government’s subpoenas of leaders in Minnesota issued during the Trump administration’s controversial immigration crackdown on the state earlier this year.

The US Department of Justice issued subpoenas to the Minnesota governor, Tim Walz, the attorney general, Keith Ellison, the Minneapolis mayor, Jacob Frey, and other local officials in the Twin Cities in January.

The department said it was investigating the officials for obstructing federal immigration enforcement. Local and state officials largely did not support the federal enforcement surge, during which federal agents killed two US citizens, Renee Good and Alex Pretti, in the streets.

The US district court for Minnesota unsealed an order from Chief Judge Patrick J Schiltz on Monday that showed the subpoenas were rejected as politically motivated. Ellison posted the unsealed order on Monday, saying the decision to quash the subpoenas was an “extremely rare step” by the court.

In the order, Schiltz wrote that the Trump administration had been “threatening and attempting to punish states and localities that have adopted ‘sanctuary’ policies”. He noted that initiating an investigation “in order to ‘harass political opponents or to coerce them into taking official action – particularly official action that the federal government cannot directly require those political opponents to take – is a blatantly unlawful and unethical use the grand-jury process”.

The court also wrote that the subpoenas violate the 10th amendment, which establishes state’s rights to self-govern on issues not specifically delineated to the federal government.

“On the one hand, the evidence that the challenged subpoenas were issued for unlawful reasons is overwhelming,” he wrote. “On the other hand, the Department has struggled – without success – to identify a single plausible investigatory justification for the subpoenas.”

He concluded that the court found the “dominant purpose” of the subpoenas was 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” and thus the court granted the motion to quash the subpoenas.

The Trump administration has repeatedly sought to go after the president’s critics, using federal powers to investigate his enemies as part of a campaign of retribution.

The justice department has also filed charges against Minnesota residents who protested against the surge, including alleging a conspiracy among 15 people who tracked Immigration and Customs Enforcement (ICE) agents and alleging violations of federal laws against almost 40 people, including two journalists, over a protest at a church.

The Department of Justice (DoJ) claimed four instances of Minnesota officials’ conduct that justified its investigations, the order notes. They included a separation ordinance written by a Minneapolis city council member, a statement by another city council member about an eviction moratorium, internal guidance from Ramsey county that advised employees not to share information with ICE agents, and training from Hennepin county about how to respond to ICE warrants and apprehensions. Notably, the department did not attempt to subpoena Minneapolis city council members.

“One would expect that, before launching a sweeping investigation into nearly the entire political structure of a sovereign state, the Department would have identified at least one instance in which a county employee actually obstructed a law-enforcement officer after being told of his or her employer’s policy,” Schiltz wrote. “Yet the Department has been unable to identify a single such instance.”

A spokesperson for the justice department said: “The Department 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.”

Walz called the ruling “a victory for the rule of law and our democracy” and stressed the need for an independent judiciary as a “pillar of our democracy”. He said he was proud to use his constitutional rights to disagree with the government during the surge.

“The US justice department is pursuing criminal investigations into the president’s political opponents,” Walz said. “This case was just one example of that, but we are seeing daily reminders of this administration’s lawlessness – in Minnesota and around the country. We all must continue to seek justice and uphold the rule of law. I will never stop exercising my constitutional rights to stand up for Minnesotans and the American freedoms that we hold dear.”

Ellison has sued the Trump administration dozens of times since the start of the second Trump term, both on cases that apply just to Minnesota and as part of coalitions with other Democratic attorneys general. He filed a lawsuit challenging the administration’s immigration crackdown on the state – known as Operation Metro Surge – on 12 January.

“The facts are clear: the Trump administration is targeting me because I’m standing up for the people of Minnesota,” Ellison said in a statement. “In America, we settle our political differences at the ballot box, and it should disturb every American that Donald Trump is weaponizing the criminal justice system against people he disagrees with. No matter how much Donald Trump threatens, targets and attacks me, I will never stop working to protect Minnesotans from Trump’s abuses of power.”

Frey said he was grateful for the court’s decision and proud to be mayor of Minneapolis, “a city of heroes where loving your neighbor is an act of patriotism that puts America first before any politician.

“No one should be targeted for questioning those in power,” 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.”