The Commonwealth of Massachusetts is set to become one of the first states to join a federal lawsuit challenging President Trump’s executive order temporarily banning immigrants from seven countries and refugees, according to a spokesman for Attorney General Maura Healey.
Lawyers in Healey’s office were finalizing court documents Monday afternoon, and planned to file a motion to intervene in the case Tuesday, with the state becoming a plaintiff, according to her aides.
The original plaintiffs are two University of Massachusetts Dartmouth professors from Iran who were detained and questioned Saturday at Logan International Airport, even though they hold green cards.
“Tomorrow, we will be joining in a lawsuit challenging Trump’s immigration order. What he did was unconstitutional & harmful to MA,’’ Healey said in a tweet Monday evening.
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Also Monday, Governor Charlie Baker referenced the pending litigation, without providing detail. The state’s involvement in court proceedings “in my opinion is the best and most significant way we can support the rule of law,” he said on WGBH.
Massachusetts would join the suit as a way to broadly assert its authority to protect Massachusetts institutions and residents similarly affected by the order that could be harmed by the president’s action, according to a person familiar with the litigation.
The institutions include hospitals, academic institutions, technological entities, or other businesses whose employees could be affected, such as UMass Dartmouth. Healey’s office would argue that the ban interferes with their interests, economic and otherwise.

“This has a big potential impact on them,” said one person familiar with Healey’s strategy.
“There was an immediate interest [by the attorney general] in getting involved.”
On Monday, during an event at a school in Dorchester, Healey comforted 12-year-old twins Muna and Muniira Abdi, who broke into tears after asking Healey, “What are you doing to make us feel like we, too, are Americans?” The girls, who were born in the United States, told Healey that recent events have made them afraid.
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The president’s order on Friday halted all refugees from coming to the United States for 120 days, barred Syrian refugees indefinitely, and prevented citizens of seven majority Muslim countries — Iran, Iraq, Yemen, Somalia, Sudan, Libya, and Syria — from entering for 90 days.
In the wee hours of Sunday in Boston, US District Judge Allison Burroughs and Magistrate Judge Judith Dein imposed a seven-day restraining order, permitting lawful immigrants who were already approved to enter the United States to continue to enter freely. The temporary ruling prohibits federal officials from detaining or deporting immigrants and refugees with valid visas or green cards or forcing them to undergo extra security screenings.
The judges had said a hearing would be held on whether to extend their order before the temporary restraining order expires Saturday. They also ordered a new, expanded complaint to be filed by Monday — a more thorough filing than the emergency complaint filed late Saturday on behalf of the UMass professors, Mazdak Pourabdollah Tootkaboni and Arghavan Louhghalam, who are both lawful permanent residents of the United States. They had attended an academic conference in Marseille and were detained at Logan upon their return, prompting the emergency lawsuit. Lawyers for the plaintiffs asked for an extension of time to file the amended complaint.
On Monday, the case was transferred to US District Judge Nathaniel M. Gorton, because Burroughs and Dein were serving as on-call judges over the weekend. Gorton, who was randomly selected to take the case, has not yet said when he will hold a hearing.
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Gorton, 78, is widely seen in the local legal community as a conservative judge. He was appointed by President George H.W. Bush in 1992.
Although Healey has not, until now, been involved in the legal case against Trump’s action, she has spoken out against it. On Sunday, she was among 16 state attorneys general who blasted Trump’s executive order in a joint statement, pledging to use their offices to fight it.
Joining Healey were attorneys general from New York, California, Pennsylvania, Washington, Hawaii, Virginia, Oregon, the District of Columbia, Connecticut, Vermont, Illinois, New Mexico, Iowa, Maine, and Maryland.
Earlier Monday, the attorney general in Washington state announced plans to challenge Trump’s order.
The American Civil Liberties Union of Massachusetts, which joined immigration lawyers in representing the UMass professors, cheered the state’s intervention.
“We welcome the fact that the Commonwealth of Massachusetts is willing to put the full weight of its leadership behind this important civil rights and civil liberties issue,” said executive director Carol Rose, “and make sure Massachusetts remains a state that defends the rights of all people and promotes the freedoms of speech and expression, due process, equal protection, and the right to travel.”
Court challenges to the executive order, now filed in at least five jurisdictions, are based on several legal theories: that Trump’s order violates due process because it takes away the rights of lawful permanent residents without any avenue for recourse; that it violates equal protection laws because it discriminates based on nation of origin and religion; and that it violates the First Amendment by being hostile to Muslims while giving preference to Christians.
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Trump said after the order was issued that Christians from the seven listed countries could be exempted from the ban.
Trump has defended his order, saying it protects America from terrorism and does not target Muslims.
He said the seven banned nations were identified by the Obama administration as “sources of terror.”
Milton J. Valencia can be reached at milton.valencia@globe.com. Follow him on Twitter@miltonvalencia.