[Photo: Immigration Protest at JFK Airport in NYC,  by Todd Maisel / NY Daily News]

Massachusetts on Tuesday joined a legal effort to block U.S. President Donald Trump's order banning travel from seven Muslim-majority countries, which the state's attorney general has said is unconstitutional.

Attorney General Maura Healey, a Democrat, said her office was joining the lawsuit filed in federal court on Friday challenging the ban and also filing its own lawsuit seeking to have the ban struck down.

"During his campaign, President Trump called for a 'complete shutdown on Muslims entering the U.S.' On Friday he acted to make good on that promise," Healey told reporters at her Boston office. "Over the past three days my office has closely reviewed the language of the order and its many impacts ... the executive order is harmful, discriminatory and unconstitutional. It discriminates on the basis of religion and national origin."

Over the weekend, U.S. District Judge Allison Burroughs of Massachusetts barred the detention or removal of approved refugees, visa holders and permanent U.S. residents entering from the 7 countries for 7 days. Her order also stopped federal officials from expelling from the country two Iranian men who teach at the University of Massachusetts at Dartmouth.

Massachusetts is following the lead of Washington state, which said on Monday it would file a lawsuit in federal court challenging the ban on constitutional grounds.

Trump's order halted travel by people with passports from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen for 90 days, and stopped resettlement of refugees for 120 days. In an interview with a Christian broadcaster over the weekend, Trump said he would give preference to Syrian Christians seeking refugee status. The White House has described the ban as necessary "to protect the American people from terrorist attacks by foreign nationals admitted to the United States."

• Thousands of people took to the streets and airports of major U.S. cities over the weekend protesting the action, which has provoked a global backlash including from U.S. allies who view the ban as discriminatory.

>  The First Amendment to the U.S. Constitution guarantees the free exercise of religion.

• On Monday, Trump fired acting U.S. Attorney General Sally Yates after she took the rare step of defying the White House and refused to defend the new travel restrictions. She said she was not convinced the order was lawful.

• Federal judges in five states blocked U.S. authorities over the weekend from enforcing Trump's order.