Three Queens residents have pleaded guilty to charges they forced women into prostitution at two massage parlors in Nassau County, Nassau prosecutors said.

Zhaowei Yin, 49; his wife Shuwen Ai, 47; and another woman, Li Fei Leng, 33 — all residents of Flushing, Queens — admitted to coercing women into performing sex acts on customers in massage parlors in West Hempstead and Franklin Square, the Nassau County District Attorney’s Office said.

Yin and Ai pleaded guilty in Nassau County State Supreme Court in Mineola Friday to charges of sex trafficking and promoting prostitution, officials said. They face three to nine years in prison, authorities said. Leng, who managed the massage parlors, pleaded guilty to those charges Tuesday and faces the same sentence.

All three waived their right to appeal, prosecutors said, and now must register as sex offenders.

Their attorneys could not immediately be reached for comment Saturday.

“The victims in this case were sexually exploited, psychologically abused and held against their wills,” Nassau County District Attorney Madeline Singas said in a written statement. “The defendants preyed on vulnerable women and, in one case, allowed a victim to be physically assaulted by a customer.”

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Both victims in the case initially were arrested and charged during undercover operations by the Nassau County Police Department, authorities said. But when investigators learned the women were victims of sex trafficking, charges against them were dropped — and the wider investigation into their traffickers launched, officials said.

The guilty pleas mark the first sex-trafficking convictions for the district attorney’s Human Trafficking Unit, which was founded last year, prosecutors said.

Singas said that between May 2013 and the end of January 2014, the trio of defendants hired two women, both of whom answered help-wanted ads published in Chinese-language newspapers.

The ads said the women would be expected to perform massages, officials said. Instead, the women were required to perform sexual services on male customers at two locations: Lucy’s Spa at 300 Hempstead Turnpike in West Hempstead, and Panda Foot Spa at 400 Franklin Ave. in Franklin Square, prosecutors said.

Both locations now are closed, officials said.

Investigators said the trafficked workers often were forced to sleep at the business. One victim never was paid for the time that she worked at the parlor, and money was deducted from the wages of the other victim for rides home, officials said.

The defendants told one of the victims that if she failed to comply with their demands, they would post a naked photograph of her on the Internet and have it published in newspapers, prosecutors said.

And when one of the victims was assaulted by a male customer, the three forced her to continue to perform the services he requested, prosecutors said.