Islands in the Pacific Ocean have turned from a tropical paradise into something of a maternity ward as pregnant Chinese women have traveled to the territory to have their babies automatically become US citizens when born.

The Commonwealth of the Northern Mariana Islands (CNMI), a US territory, has been flooded with “birthing tourists” since 2009, when former President Barack Obama allowed for a visa-waiver program for Chinese nationals. There are about 1,000 companies that offer birth tourism in the islands, other US territories, and on the US mainland, per the New York Post.

There are around 1.5 million American babies being raised in China by Chinese parents who traveled to the US or its territories in order to birth their children, according to analysts who spoke to the outlet. Republican lawmakers have demanded an accounting of how many people Chinese nationals have taken advantage of how the system has been laid out for birth citizenship.

“The concern is about these children born to Chinese parents — do the parents have connections to the Chinese Communist Party, which is an adversarial government to the US?” said Chris Chmielenski, who is the president of the nonprofit Immigration Accountability Project. “They know there is an industry out there that makes gobs of money to specialize in birth tourism but there is no report from the federal government telling you how many people have been born as a result of this,” he added.

A large portion of the children who were born back when Obama shifted the visa policy will be eligible to vote in upcoming elections. They will also be able to petition at age 21 to have parents and siblings obtain green cards to the US.

“It’s not just the voting aspect, it’s the chain migration laws,” said Chmielenski. “If their family could afford the prices charged for this birth tourism scheme, there’s a good chance they can afford a residence in the US. That raises concerns. Most wealthy Chinese nationals tend to have connections to the government there.”

Companies from China have capitalized on the opportunity, with expectant mothers being offered a getaway experience to have their child. “Create beautiful memories while having an American baby,” a homepage of the company website for Global Baby 8 says.

In a letter on March 9, a letter to Trump officials from Republican lawmakers raised the concern, and demanded that there be an accounting of how many Chinese nationals have come to the US for birthing tourism.

The letter demanded federal data about the problem and slammed the “absurd birthright citizenship policies and the resulting birth tourism industry,” saying it was “alarming.”