From South China Morning Post:
Other than hotels, massage parlours are the number one venue for sex trafficking in the United States, according to Polaris, a leading anti-trafficking group.
More than 9,000 illicit massage businesses are operated across the country, representing a US$2.5 billion industry, Polaris says. The spa workers are often mothers who come from poor, rural parts of China, according to Polaris.
They are enticed by labour agencies selling the idea that they can work as a legitimate masseuse and send money back to their families. Once they arrive, they are entirely dependent on their employer.
Many of the parlours are registered and operated by an employee who serves as a “front,” making it difficult if not impossible to trace the ultimate owner or hold those who benefit financially accountable.
https://www.scmp.com/sport/other-sport/article/2187688/robert-kraft-affidavit-patriots-owner-visited-orchids-asia-spa-sex