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.