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A couple is due in federal court in Maine for a detention hearing related to their indictment on charges of using Chinese nationals in a sex-trafficking operation.

Court officials say 37-year-old Sou Chao Li and his wife, 37-year-old Derong Maio, of Concord, New Hampshire, are due in court in Portland Thursday at 1 p.m. They’re accused of running the operation in Maine, Vermont and their home state.

An indictment that was unsealed earlier this month indicated the couple used a messaging system popular in China to lure women to come to the United States on tourist visas to work in the sex trade. Authorities say the scheme involved at least 27 women.

A phone message to an attorney for Li was not returned. Defense attorneys haven’t comment much on the case.