If set in motion, the order will end the automatic citizenship of children born in the US to non-citizen parents.

Eighteen states and two cities, San Francisco and Washington, D.C., challenged the order in Federal District Court in Massachusetts, arguing that birthright citizenship under the 14th Amendment is “automatic” and that neither the president nor Congress has the constitutional authority to revise it, reported The New York Times.

Four other states filed a second lawsuit in the Western District of Washington, the newspaper reported.

Announcing the suit,  California Attorney General Rob Bonta said: “The President’s executive order attempting to rescind birthright citizenship is blatantly unconstitutional and quite frankly, un-American."

In his statement, he asked the court to immediately block the order from taking effect.

"The President has overstepped his authority by a mile with this order, and we will hold him accountable," Bonta said.

The executive order signed by Trump specified that a child born in the USA will be granted citizens if at least one parent must be a US citizen, a legal permanent resident (green card holder), or a member of the US military.

"The Secretary of State, the Attorney General, the Secretary of Homeland Security, and the Commissioner of Social Security shall take all appropriate measures to ensure that the regulations and policies of their respective departments and agencies are consistent with this order, and that no officers, employees, or agents of their respective departments and agencies act, or forbear from acting, in any manner inconsistent with this order," read the White House order.

What is Birthright citizenship?

As per the American Immigration Council website, Birthright citizenship is a legal principle under which citizenship is automatically granted to individuals upon birth.

In the United States, birthright citizenship is guaranteed by the Fourteenth Amendment to the Constitution, the website said.