The Trump administration on Thursday formally issued a rule allowing customs officials to deny entry to travelers whom they suspect are headed to the U.S. for the sole purpose of giving birth on American soil.

A rule issued by the State Department marks the administration's first formal effort to cut down on the practice known as "birth tourism," which President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE has heavily criticized and suggested should be a reason for ending birthright citizenship.

"This rule establishes that travel to the United States with the primary purpose of obtaining U.S. citizenship for a child by giving birth in the United States is an impermissible basis for the issuance of a B nonimmigrant visa," the statute reads.

ADVERTISEMENT

"Consequently, a consular officer shall deny a B nonimmigrant visa to an alien who he or she has reason to believe intends to travel for this primary purpose," it continues.

The White House said in a statement that "the birth tourism industry threatens to overburden valuable hospital resources and is rife with criminal activity, as reflected in Federal prosecutions."

"Closing this glaring immigration loophole will combat these endemic abuses and ultimately protect the United States from the national security risks created by this practice," the statement read.

It's unclear how customs officials are to determine whether a traveler is headed to the U.S. for the purpose of giving birth on U.S. soil, though U.S. officials hinted to Axios earlier this week that Thursday's rule could be just the first in a line of actions against birth tourism.

"Rome wasn't built in a day," a senior official told the news outlet. "Just the legal recognition that this is improper and wrong and not allowed is a significant step forward."

"This change is intended to address the national security and law enforcement risks associated with birth tourism, including criminal activity associated with the birth tourism industry," a State Department official added to Axios.

ADVERTISEMENT

Lawmakers have previously questioned whether the administration has the right to curb birthright citizenship through executive action, with some — including allies of the president — believing that doing so would require a change to the Constitution.

“I am not a lawyer, but it seems to me it would take a constitutional amendment to change that as opposed to an executive order," Sen. Chuck Grassley Charles (Chuck) Ernest GrassleySenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE (R-Iowa) said of the president's criticism of birthright citizenship in 2018.

—Updated at 12:27 p.m.