A Mexican citizen pleaded guilty Friday to smuggling women into the U.S. to work as prostitutes at brothels in 13 cities across the country, including Dallas and Fort Worth.

Juan Balderas-Orosco, 34, managed an Austin brothel as part of a national prostitution ring that catered to illegal immigrants who paid $40 each to have sex with the women, according to court records filed by prosecutors in Austin federal court.

Some of the women reported having sex with as many as 40 men a day, prosecutors said.

"The prostitutes reported they were not free to leave the brothels on their own, and the brothel operators were usually armed with firearms," according to court records. Those records also noted that the prostitutes were moved weekly by bus or plane to other brothels operated by the ring across the country.

The enterprise began to unravel in November 2002 when investigators searched the Austin brothel and arrested several prostitutes, who identified Mr. Balderas, known as "Johnny."

Mr. Balderas was arrested in June when Immigration and Customs Enforcement agents raided establishments in Dallas, Austin and Oklahoma City.

Mr. Balderas told investigators that he was working for Maria Camacho-Teran, who owned the Dallas brothel. Ms. Camacho is also under indictment on smuggling charges and is awaiting trial in Austin. Mr. Balderas faces a maximum federal prison sentence of 30 years.

Court records did not identify the location of the Dallas and Fort Worth brothels.

His lawyer, Kristin Etter, said the case was a symptom of a broken immigration system. With limited opportunities for immigrants to come to the U.S., some "are pushed into this underground economy and forced into these kinds of jobs," she said.

The Associated Press contributed to this report.