US police have broken up two human trafficking rings which smuggled hundreds of South Korean women into California to work as prostitutes.
Women are forced into prostitution to repay their debts
They arrested about 50 people and are questioning around 150 women after taking them into protective custody.
The women were working in dozens of brothels disguised as acupuncture clinics and massage parlours in Los Angeles and San Francisco.
This could be one of the largest human trafficking cases prosecuted in the US.
About $3m (£1.7m) was recovered in the operation.
Police are now questioning the women to piece together the details of the large smuggling operation.
"This type of criminal organisation exploits the hopes and dreams of immigrants," said US attorney Debra Wong Yang at a press conference in Los Angeles.
The women were reportedly charged $16,000 to be smuggled into the US.
They were repaying their debts by working as prostitutes and giving their earnings to the ring.
Those arrested have been charged with conspiracy to harbour illegal aliens for prostitution and transporting them across state lines, as well as money laundering and sex trafficking.
The two rings operated separately, one in San Francisco and one in southern California.
But investigators believe the ringleaders knew each other and were lending each other some of the workers.
"If they needed a couple of extra women in San Francisco, the (Los Angeles) ring would send them up," said Thom Mrozek, spokesman for the US attorney's office in Los Angeles.
Some of the women are believed to have entered the country through the Mexican and Canadian borders, while others used illegally obtained tourist visas.