President Donald Trump's executive order on birthright citizenship is a "flagrantly illegal" attempt to redefine a right "enshrined in the very fabric of our country," argued a lawsuit filed overnight in Massachusetts federal court.

The lawsuit -- brought by an undocumented expectant mother who is due in March and two nonprofit groups -- is expected to be one of the many legal challenges to the executive order that seeks to reinterpret the 14th Amendment's guarantee of citizenship to nearly every person born in the United States.

"This unprecedented attempt to strip citizenship from millions of Americans with the stroke of a pen is flagrantly illegal. The President does not have the power to decide who becomes a citizen at birth," the lawsuit said.

The plaintiffs argued that birthright citizenship is not only guaranteed in the 14th Amendment but has also been consistently codified into federal law; stripping away that right would be "overwhelming and devastating," the lawsuit argued.

"Those victimized in this way by the EO would be shorn of their national identity, stigmatized in the eyes of those who should be their fellow citizens, and forced to live with the shame, uncertainty, and fear that comes with potential banishment from their native country. Many would be rendered immediately stateless," the lawsuit said.

The lawsuit asked for the Massachusetts District Court to declare the executive order unconstitutional and issue an injunction preventing the enforcement of Trump's directive.

The ACLU also filed a lawsuit challenging Trump's executive order.

-ABC News' Peter Charalambous

President Donald Trump and his family attended the third inaugural ball of the evening, the Starlight Ball.

They were joined onstage by Vice President JD Vance and his wife, Usha.

Just before midnight on President Donald Trump's first day back in office, two convicted Jan. 6 rioters walked out of the Central Detention Facility in Washington, D.C.

Paul Ingrassia, who is the incoming White House liaison with the Department of Justice, emerged after more than an hour inside the jail and said that Andrew and Matthew Valentin -- two brothers from Pennsylvania arrested for assaulting law enforcement during the attacks on the Capitol -- were processed and had left the facility.

The brothers had just received their sentences of 2.5 years apiece and taken into custody to serve them out on Jan. 17. They pleaded guilty in September 2024.

They are the only two who are expected to be released tonight, according to Ingrassia. However, family members outside of the facility said that they remain hopeful.

According to the most recent numbers from the DOJ, a total of eight pardoned inmates — out of the over 1,500 pardoned — are incarcerated inside the facility.

ABC News has not yet confirmed the release beyond the liaison's statement.

-ABC News' Jay O'Brien, Alexander Mallin, Katherine Faulders and Briana Stewart

During his appearance at the Commander-In-Chief inaugural ball on Monday evening, President Donald Trump spoke with troops deployed in South Korea displayed on a projector screen.

"Hello, everybody. How are we doing over there? How's Kim Jong Un doing? How are you?" Trump said.

Trump told the troops that he has a "pretty good relationship" with the North Korean leader despite his "bad intentions."

"So, could I ask you, how is it going in South Korea right now? How is it doing? You have somebody with pretty bad intentions, I guess. You know, you would say that although I developed a pretty good relationship with him. But he's a tough cookie," Trump said.

In the weeks after winning the election in November, Trump said in a post on Truth Social that imposing tariffs would be one of his first acts as president.

"On January 20th, as one of my many first Executive Orders, I will sign all necessary documents to charge Mexico and Canada a 25% Tariff on ALL products coming into the United States," he wrote.

However, he opted not to include tariffs as one of his top priorities. Instead, during his inauguration speech, he announced the creation of an External Revenue Service that would be in charge of collecting tariffs and other revenue from foreign nations.

Then, later in the evening, he expressed that his administration was "thinking in terms" of imposing 25% tariffs on Mexico and Canada on Feb. 1.

While he has also previously mentioned imposing tariffs on China, he did not mention it during his remarks in the Oval Office on Monday.