The State Department on Thursday unveiled new rules that could make it more difficult for pregnant foreign nationals to travel to the United States using tourist visas, citing security concerns.

The rules, which will become effective on Friday, are an attempt to crack down on "birth tourism," or the practice of giving birth in the United States in order to obtain U.S. citizenship for a child. They apply to B visas, or those issued to nonimmigrants.

"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," she said.

The Trump administration has sought to limit immigration to the United States, and President Donald Trump has been particularly critical of birthright citizenship, or the right of those born in America to citizenship. The 14th Amendment to the Constitution grants citizenship to "all persons born or naturalized in the United States."

Activists criticized the administration's move. Adrian Reyna, the strategy director of United We Dream, a nonprofit immigration group, said in a statement that "Trump continues to find new ways to try to divide and attack families."

"Discriminating against pregnant individuals by blocking them from coming to visit the country does nothing but keep people from their loved ones," Reyna said. "This rule is based on Trump's racist fixation on ending birthright citizenship and essentially stopping the movement of people into this country."