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May 1, 2015, 2:50 AM UTC / Updated May 1, 2015, 11:39 AM UTC / Source : NBC News

Ten customers of a Chinese "birth tourism" operation who defied orders to remain in the United States as witnesses have been hit with charges of obstruction of justice and contempt of court, federal authorities said on Wednesday.

The women paid up to $50,000 to give birth on American soil — making their newborns automatic U.S. citizens — as part of what investigators say is a growing underground industry.

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Couples allegedly lied on their visa applications to get into the country. Some of them claimed they were indigent, socking California hospitals with the bills for the delivery.

NBC News was on the scene in March when federal agents swept into a luxury apartment in Irvine, California, where several units doubled as so-called maternity hotels.

The women found there and at several other sites were detained and treated as material witnesses in an ongoing probe of the scheme's alleged ringleaders.

Court orders required that 29 of the women and some of their spouses stay in the United States, but a third of them fled and are believed to be back in China.

One woman was busted at the airport a week ago with her infant son as she tried to make a break for it, the Riverside Press-Enterprise reported.

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