REDWOOD CITY -- A Union City man has pleaded not guilty to pimping women at a brothel discovered in a San Bruno apartment complex during a federal sex trafficking sweep, a prosecutor said Monday.

Senhsu Yang, 35, entered his plea Friday in San Mateo County Superior Court and was being held in Redwood City in lieu of $20,000 bail, according to Chief Deputy District Attorney Karen Guidotti.

Yang was arrested July 26 at a San Bruno apartment complex that authorities suspect is part of a Bay Area sex trafficking ring. Authorities said they found about $1,000 in cash and discovered two women there who were working as prostitutes.

Defense attorney Alex Park declined to comment on the case, noting he has just begun his investigation.

Police took Yang into custody as part of an annual anti-trafficking operation that is coordinated by the FBI.

As part of Operation Cross Country, police freed 12 children from prostitution and arrested 21 pimps in Bay Area cities ranging from Oakland to San Jose.

A total of 105 children were rescued and 150 pimps arrested in 76 cities across the United States.

Yang is due back in court Oct. 24, Guidotti said. He faces one felony count of pimping.

Contact Joshua Melvin at 650-348-4335. Follow him at Twitter.com/melvinreport.