IRVINE – A Chinese woman, a federal witness in an ongoing investigation into the birth tourism industry, is under arrest after trying to leave the U.S. with her newborn American son.

Ying Wu, 31, was taken into custody April 15 at Los Angeles International Airport by Homeland Security Investigations agents as she, her husband and the baby prepared to board a plane to Beijing.

Her arrest comes amid a large-scale federal investigation of several Southern California companies accused of persuading pregnant Chinese women to lie on visa applications so their babies can be born on U.S. soil.

At least one company seems to be continuing to solicit such business, with a website that’s active in Taiwan. The websites for other companies connected to the early March crackdown aren’t active.

Wu is a material witness in the government’s case. She was arrested after being ordered to remain in the U.S., said Thom Mrozek, a spokesman for the U.S. Attorney’s Office for the Central District of California.

About two dozen women have been retained as material witnesses.

Wu, who on Friday appeared in a Santa Ana federal court, is free on a $10,000 unsecured bond. She is under house arrest at an undisclosed location, wearing a GPS monitoring device, Mrozek said.

Her husband, who has not been identified, and their baby also remain in the U.S., Mrozek added.

The arrest has been upsetting for Wu, said her Newport Beach attorney, T. Edward Welbourn.

“She is in some turmoil right now … She wants to return to her family,” Welbourn said Wednesday.

Wu’s arrest follows a March raid by federal agents of about three dozen residences in Irvine, Mission Viejo, Rancho Cucamonga, Rowland Heights and Walnut connected to the burgeoning maternity tourism industry.

Authorities are looking for evidence of visa and tax fraud, money laundering and conspiracy involving three suspected maternity tourism companies, You Win USA Vacation Resort, USA Happy Baby Inc. and Star Baby Care. No charges have been filed against any company.

“Our focus is doing forensics on computers and a broad array of documents,” said Virginia Kice, a spokeswoman for U.S. Immigration and Customs Enforcement. “We have interviewed a significant number of witnesses and are in the process of culling through the evidence.”

Star Baby Care is the only one of the three companies with an active website. On Wednesday, the site touted Irvine as an exceptional place for mothers to give birth, mentioning the city’s low crime rate and proximity to shopping and restaurants.

The residences raided in March housed women believed to have each paid tens of thousands of dollars to maternity tourism companies that promoted American citizenship, free education and other perks for U.S.-born babies.

As part of the package, women were told their children would get Social Security numbers and U.S. passports that they could take with them when they left the U.S. After the U.S.-born children reach adulthood, they can then apply for visas for family members living abroad.

It is unclear how many of the women have given birth since March and returned to China or still remain in Southern California.

Maternity tourism operators have advertised their services in China, charging fees ranging from $15,000 to $50,000, according to affidavits from ICE.

The more the client paid, the more perks the women got, including trips to Disneyland, shopping malls and outings to a firing range.

Authorities estimate those who ran You Win USA Vacation Resort in Irvine made $2 million in 2013 and helped women give birth to 400 children in Orange County, the affidavits state.

It is not illegal for foreign nationals to give birth in the United States.

But authorities allege operators instructed their clients to deceive the federal government on visa applications and make false claims of indigence to get lower fees for health services.

In some cases, according to the affidavits, the women were told what to wear to hide their pregnancies at airports to avoid questions about the purpose of their visits.

Contact the writer: 714-796-7767 or sschwebke@ocregister.com. On Twitter: @thechalkoutline