In addition to expanding the current travel ban, Trump recently announced new visa restrictions for pregnant women, in order to discourage “birth tourism.”

“Birth tourism” is the practice in which women travel to the US solely to give birth, so their children can have a much-desired US passport. If consular officers believe a visa applicant is coming to the US to give birth, they will now have to prove that they are visiting the country for medical treatment, and can afford that treatment.

The new measure is somewhat controversial, as consular officers aren’t allowed to ask about a woman’s pregnancy or plan to become pregnant during visa interviews. Therefore, it’s unclear how officers would determine whether or not a woman is coming to the US to give birth. It is also unclear how border agents will determine if a woman is pregnant or not when going through customs.

It’s undisputable, though, that birth tourism has become a major US industry, with some companies promoting hotel rooms and medical care specifically for expectant foreign mothers — many of whom come from Russia and China, according to AP News.

Birthright citizenship, in which a person who is born in the US automatically becomes a citizen regardless of their parents’ status, is inscribed in the US Constitution.