The phenomenon of so-called anchor babies has fueled criticism from advocates of tougher immigration laws who are concerned that foreign adults are using their children to secure permanent residency in the United States and from there, access to public benefits.

The indictments include an array of charges, including visa fraud, wire fraud and identity theft, against owners of the birth-tourism agencies that are accused of enabling thousands of Chinese women to come explicitly to give birth to American children.

“Statements by the operators of these birthing houses show contempt for the United States, while they were luring clients with the power and prestige of U.S. citizenship for their children,” Nick Hanna, United States attorney in Los Angeles, said in a statement. “Some of the wealthy clients of these businesses also showed blatant contempt for the U.S. by ignoring court orders directing them to stay in the country to assist with the investigation, and by skipping out on their unpaid hospital bills.”

There are no official figures for how many babies are delivered to tourists on American soil. The Center for Immigration Studies, a group that supports restricting immigration, puts the number at about 36,000 annually in a 2015 report.

“The fact that we have no idea of the scale of birth tourism is a problem in and of itself,” said Jessica Vaughan, director of policy studies at the center in Washington. “We should not tolerate an entire industry that encourages people to come here for the sole purpose of having a child who leaves with a U.S. passport.”

In recent years, the practice has prompted some lawmakers, who have opposed children of undocumented immigrants automatically becoming citizens, to propose repealing birthright citizenship, which is enshrined in the 14th Amendment of the Constitution.

President Trump last year claimed erroneously that the United States is the “only country in the world” that automatically confers citizenship to anyone born in the country. In fact, it is one of at least 30 countries that do so.