A New Hampshire husband and wife accused of using Chinese nationals in a sex-trafficking operation in Maine, New Hampshire and Vermont are due in court.

Detention hearings are scheduled Tuesday in U.S. District Court in Portland, Maine, for 37-year-old Sou Chao Li and his wife, 37-year-old Derong Maio, of Concord, New Hampshire.

An indictment unsealed when they were arrested Thursday indicates they used WeChat, a messaging system popular in China to entice women to come to the U.S. on tourist visas to work in the sex industry.

The indictment indicates at least 27 women were involved in the operation.

Each is charged with one count of conspiracy to engage in interstate transportation and travel for prostitution; two counts of sex trafficking by fraud and coercion; and five counts of interstate transportation for prostitution. Li also is charged with possessing a victim’s passport as part of the sex trafficking scheme.

Li and Maio operated an interstate prostitution enterprise from July 2016 to at least February 2018, according to an indictment announced by U.S. Attorney Halsey B. Frank of the District of Maine and Assistant Attorney General Eric Dreiband of the Justice Department’s Civil Rights Division.

Li and Maio recruited Chinese women to travel to Maine, then caused them to engage in prostitution by controlling their movements and isolating them at rented homes and hotels, according to the indictment.

The indictment charges that Maio used WeChat, among other means of communication, to recruit Chinese women “to work in the prostitution industry with promises of personally earning hundreds of dollars a day at various locations operated by the defendants.”

Once the women were being trafficked, the defendants “deprived them of (personal) documents, food, clothing and room keys and other things to ensure they were unable to leave such locations without the consent and assistance of the defendants or their co-conspirators.” The indictment doesn’t name the co-conspirators.

The indictment charges that the defendants rented a single-family home at 5 Verrill St. in Portland, in a residential neighborhood off outer Forest Avenue, from June 1 to July 18, 2016; and an apartment at 977 Brighton Ave. in Portland, near the Westbrook line, starting July 29, 2016; as well as two homes in Manchester, New Hampshire.

They also rented hotel rooms on multiple dates at the Travelodge, 1200 Brighton Ave. in Portland; the Days Inn, Comfort Inn and Econo Lodge, all near the Maine Mall in South Portland; and the Days Inn in Kittery; as well as hotel rooms in Portsmouth and Dover, New Hampshire; and in South Burlington and Colchester, Vermont.

Most of the women came to the United States on tourist visas that didn’t allow them to work while here, according to the indictment. They spoke little or no English and had no other contacts in Maine or neighboring states. Some worked at jobs other than prostitution when they first arrived “but were unable to earn a wage substantial enough to repay debts associated with their travel to the United States.”