Here's a look at the arguments and implications of the lawsuit, which Attorney General Maura Healey has joined on behalf of the state of Massachusetts.
BOSTON -- Massachusetts Attorney General Maura Healey filed a brief on Tuesday joining a federal court case challenging President Donald Trump's executive order on immigration.
"The executive order is harmful, discriminatory and unconstitutional," Healey said at a press conference. "It discriminates on the basis of religion and national origin, denies our residents access to due process and equal protection of the law and violates federal immigration law."
In her brief, Healey argues that Trump's order "represents a stark and troubling departure from this nation's founding principles."
Trump's order bars travel into the U.S. for 90 days by non-U.S. citizens from seven predominantly Muslim countries: Iran, Iraq, Syria, Sudan, Libya, Yemen and Somalia. It suspends the admission of all refugees for 120 days and Syrian refugees indefinitely.
U.S. District Court Judge Allison Borroughs, in a ruling issued around 2 a.m. Sunday, put in place a temporary one-week stay on Trump's order detaining and deporting people traveling from the seven countries. The court will have to issue a more permanent order after the week is up.
A hearing is scheduled for Friday at U.S. District Court in Boston.
The ACLU and private attorneys, who filed the original court challenge, filed an amended complaint on Wednesday to include additional plaintiffs.
"This executive order is illegal, it's unconstitutional and it's unpatriotic," said Carol Rose, president of the ACLU of Massachusetts. "We believe it will be struck down."
Here's a look at the legal action and what it means.
Can I read the briefs?
Not easily. Although there can be little doubt as to the public interest and importance of the case, because it is officially listed as an immigration case, U.S. District Court Judge Nathaniel Gorton has ruled that the briefs will not be made available online through the U.S. District Court website.
The ACLU, which asked Gorton to allow electronic access, posted its brief online.
Healey's brief is available to the public only on a single computer at the Moakley federal courthouse in Boston.
Who are the plaintiffs?
The original complaint was filed by the ACLU of Massachusetts and private attorneys on behalf of two Iranian associate professors from the University of Massachusetts at Dartmouth, Mazdak Pourabdollah Tootkaboni and Arghavan Louhghalam, who were detained at Logan Airport.
The expanded complaint includes four more individuals and Oxfam America. All the individuals are from Iran and are either lawful permanent residents of the U.S. or students with visas. Oxfam America is a social justice group that works to alleviate poverty around the world and brings people from different countries to talk to U.S. policymakers, including from several countries affected by Trump's executive order.
Two plaintiffs -- Fatemeh Yaghoubi Moghadem, who has a bachelor's degree in graphic design, and Babak Yaghoubi Moghadem, an engineer who develops medical devices -- are a sister and brother who fear visiting family in Iran in case they cannot return home. Plaintiff Ali Sanie is a grocery store cashier who planned to return to Iran to get surgery for neck pain but delayed travelling because of the ban. Zahrasadat Mirrazi Renani is a first-year doctoral student in linguistics at UMass Amherst who wants to visit family in Iran and attend a professional conference in Canada. Leily Amirsardary graduated from Wellesley College in 2016 and is starting a Boston-based luxury women's shoe and accessory company. She wants to travel to countries where her products are sourced, including Italy.
Who are the defendants?
The defendants are Trump, the U.S. Department of Homeland Security, U.S. Customs and Border Protection, and top officials at those agencies.
What is the role of the Commonwealth of Massachusetts?
Healey asked the judge to allow her to intervene on the side of the plaintiffs, on behalf of the state of Massachusetts and the University of Massachusetts.
Healey argues that Massachusetts residents, students and employers have a stake in the executive order. At a press conference, Healey said Trump's order provides "serious interference with our economic lifeblood as a state."
In her brief, Healey wrote that the executive order will "hinder the free exchange of information, ideas and talent between the affected countries and the Commonwealth, including at the Commonwealth's many educational institutions; will harm the Commonwealth's life sciences, technology, health care, and other industries, as well as innumerable small businesses throughout the Commonwealth; and will inflict economic harm on the Commonwealth itself."
Healey wrote that Massachusetts is home to more than 1 million immigrants, including thousands from the seven affected countries, and to tens of thousands of international students. It welcomes 2,000 refugees annually. She argued that hindering travel and immigration will hurt state businesses and institutions, particularly in higher education and health care. It will harm students and faculty who cannot attend professional conferences or visit family. It could make the state less competitive globally and discourage international conferences from being held here.
The University of Massachusetts has 160 faculty, researchers and staff and 350 students from affected countries.
Gov. Charlie Baker, a Republican, said his office worked with Healey's office on the brief and supports the legal challenge.
What are the plaintiffs asking for?
They are asking the court to overturn Trump's executive order by declaring it unconstitutional and to forbid U.S. officials from detaining or deporting anyone, or barring anyone from traveling, based on the order.
What are their legal arguments?
Both the ACLU team and Healey say the executive order fulfills Trump's campaign promise to institute a "Muslim ban." "If an Executive Order looks like a Muslim ban, acts like a Muslim ban, and has been talked about as a Muslim ban, then it's probably a Muslim ban," wrote lawyers for the plaintiffs.
Healey wrote that the executive order "effectively labels many Massachusetts residents as unworthy of certain rights and immigration benefits and as threats to our society simply on the basis of their religion or nation of origin, and thus unfairly and unreasonably casts a shadow of stigma and fear that will follow them to work, school, and elsewhere." She added: "The sweeping Executive Order was motivated by animus against the Islamic faith and those who are Muslim."
Trump officials disagree with the characterization, saying the ban applies to all residents of countries likely to pose a national security threat to the U.S.
Attorneys for Healey and the plaintiffs cite Trump's policy of favoring refugee admission of religious minorities -- in these countries, non-Muslims -- as well as Trump adviser Rudy Giuliani's comments that Trump wanted to find a legal way to implement a Muslim ban to argue that the order unconstitutionally discriminates based on religion.
The plaintiffs and their attorneys argue that the travel ban violates First Amendment rights prohibiting religious discrimination; violates free speech rights by prohibiting academics and scientists from engaging in an exchange of ideas; violates rights to due process and equal protection; and violates laws governing administrative procedures. Healey also argues that the law violates Massachusetts' sovereign commitment as a state not to discriminate based on religion and national origin in offering employment and educational opportunities.
Has the Trump administration responded?
The United States has not yet filed any response briefs in the case. Generally, Trump has defended the travel ban as a necessary step to keep Americans safe while his administration crafts new vetting procedures for immigrants and refugees. Over the weekend, U.S. officials said they would admit green card holders back into the country through a waiver process.
Is Massachusetts the only state to join a lawsuit against Trump's order?
No. The attorney general of Washington State also challenged Trump's travel ban in court.