WASHINGTON (AP) — The Trump administration on Thursday imposed new visa rules aimed at restricting "birth tourism," in which women travel to the United States to give birth so their children can have U.S. citizenship.

Applicants will be denied a tourist visa unless they can prove they must come to the U.S. to give birth for medical reasons and they have money to pay for it — not just because they want their child to have a passport.

"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," White House press secretary Stephanie Grisham said in a statement. "It will also defend American taxpayers from having their hard-earned dollars siphoned away to finance the direct and downstream costs associated with birth tourism. The integrity of American citizenship must be protected."

The practice of traveling to the U.S. to give birth is fundamentally legal, although there are scattered cases of authorities arresting operators of birth tourism agencies for visa fraud or tax evasion. And women are often honest about their intentions when applying for visas and even show signed contracts with doctors and hospitals.

The State Department "does not believe that visiting the United States for the primary purpose of obtaining U.S. citizenship for a child, by giving birth in the United States — an activity commonly referred to as 'birth tourism' — is a legitimate activity for pleasure or of a recreational nature," according to the new rules, which were published Thursday in the Federal Register and take effect Friday.

While the new rules deal specifically with birth tourism aimed at wealthy immigrants coming largely from China and Russia, the Trump administration also has  turned away pregnant women coming over the U.S.-Mexico border as part of a broader immigration crackdown. Those women were initially part of a "vulnerable" group that included others like small children who were allowed in, while tens of thousands of other asylum seekers have been returned to Mexico to wait out their cases.

President Donald Trump's administration has been restricting all forms of immigration, but Trump has been particularly plagued by the issue of birthright citizenship — anyone born in the U.S. is considered a citizen, under the Constitution. The Republican president has railed against the practice and threatened to end it, but scholars and members of his administration have said it's not so easy to do.

Regulating tourist visas for pregnant women is one way to get at the issue, but it raises questions about how officers would determine whether a woman is pregnant to begin with and whether a woman could get turned away by border officers who suspect she may be just by looking at her.

And critics of the new policy say it could put pregnant women at risk.

Consular officers don't have the right to ask during visa interviews whether a woman is pregnant or intends to become so. But they would still have to determine whether a visa applicant would be coming to the U.S. primarily to give birth.

Birth tourism is a lucrative business in both the U.S. and abroad. Companies take out advertisements and charge up to $80,000 to facilitate the practice, offering hotel rooms and medical care. Many of the women travel from Russia and China to give birth in the U.S.

The U.S. has been cracking down on the practice since before Trump took office.

"An entire 'birth tourism' industry has evolved to assist pregnant women from other countries to come to the United States to obtain U.S. citizenship for their children by giving birth in the United States, and thereby entitle their children to the benefits of U.S. citizenship," according to the State Department rules.

There are no figures on how many foreign women travel to the U.S. specifically to give birth. The Center for Immigration Studies, a group that advocates for stricter immigration laws, estimated that in 2012 about 36,000 foreign-born women gave birth in the U.S. and then left the country.

"This rule will help eliminate the criminal activity associated with the birth tourism industry," according to the rules. "The recent federal indictments describe birth tourism schemes in which foreign nationals applied for visitor visas to come to the United States and lied to consular officers about the duration of their trips, where they would stay, and their purpose of travel."

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Associated Press Writer Ellen Knickmeyer contributed to this report.