HOUSTON – Sometimes going undercover in Texas means no cover at all.

Houston police, long thwarted in their campaign against prostitution by an internal policy that barred officers from removing their clothes, have reaped results by shedding that unwritten rule.

The change in tactics that allows vice squad officers to undress in pursuit of evidence is part of a crackdown on suspected brothels that advertise themselves as day spas, lingerie modeling studios, massage parlors and “stress relief clinics.”

Two investigations using the new rules have resulted in organized crime charges against six business proprietors and dozens of misdemeanor prostitution charges.

Police largely built their investigation through traditional detective work, such as surveillance, but Harris County prosecutor Ted Wilson said the department’s ability to pose as naked clients was particularly useful.

“It helped,” Wilson said on Monday. “It’s something they can do, if necessary, to gather sufficient evidence.”

Knowing police were not allowed to disrobe meant sex workers could ask customers to undress before propositioning them to determine if a potential client was an undercover officer.

The series of arrests in November are seen as a signal that Houston police have closed that loophole.