According to the eight-count indictment, the operation was intricate for its organization. Among those indicted were the people owed the bondage debts of the women brought from Bangkok. Others who were indicted served as “house bosses” in cities like Austin, Tex.; Chicago; Dallas; and Los Angeles, where they used apartments, hotels, houses and massage parlors for prostitution. Still others served as money launderers, putting cash returns into bank accounts, and facilitators, who took care of details like flying the women from city to city.

While still in Thailand, the women were usually told that they would work as prostitutes, the indictment said, but the terms of the deals shifted substantially once they arrived in the United States. Threats were made. Bondage debts suddenly skyrocketed. Some women were even told to have plastic surgery to make them more “appealing” to customers, then ordered to reimburse the cost of surgery as part of their ever-growing debt.

The authorities said the women were kept isolated and were not allowed to leave the prostitution houses without being accompanied by one of the ring organizers. The hours of prostitution often ran all day, every day.

Officials said some of the women are now being helped by agencies to find housing and other assistance. But their immigration status in this country is uncertain; many were brought here with visas obtained using false information, the authorities said, including fictitious occupations and phony backgrounds. One of the main reasons women had accepted such deals in the first place, the officials said, was the promise of a legitimate visa.

By Thursday, 20 of the 21 accused — all of whom were described as organizers of the operation — had been arrested in various cities. More than a dozen others were arrested in connection with the ring last fall, officials said. In making the latest arrests in places like Chicago, Houston and San Diego, the authorities said they seized hundreds of thousands of dollars in cash, along with cellphones, weapons and condoms. Lawyers for those arrested could not immediately be reached. Ten of the accused are Thai nationals; the rest are American citizens, the authorities said.