In their ongoing battle against the city's entrenched gangs, Los Angeles prosecutors and police increasingly have relied in recent years on a favorite legal weapon: court-ordered injunctions.

The injunctions aim to severely curtail gang activity by, among other things, prohibiting gang members and their associates from socializing with each other, carrying weapons or wearing certain clothing anywhere inside of so-called "safe zones" that typically encompass the neighborhoods where the gangs are active.

There are nearly 50 injunctions in effect in Los Angeles. City officials routinely credit them with playing a large role in the gains they have made in recent years on tamping down gang violence, drug dealing and other crimes. LAPD officers work with lawyers from the city attorney's office to identify and notify the gang members and associates who must adhere to injunction rules. Violators are commonly arrested.

Now, a federal lawsuit filed earlier this month in Los Angeles has taken aim at the nighttime curfews written into 21 of the injunctions. Olu Orange, the attorney who filed the lawsuit, said the terms of the curfews, which prohibit going outside after 10 p.m., are so broad and vague as to violate a person's constitutional rights.

The city, Orange said, has willfully ignored a 2007 California Supreme Court ruling that found a similarly worded gang curfew violated people's due process rights. In that ruling, the court found an injunction against an Oxnard gang did not adequately define what it meant for someone to be "outside" during the curfew hours.

The wording was "so vague that men of common intelligence must necessarily guess at its meaning," the court found.

Other gang injunctions in Los Angeles also impose curfews, but use wording that is more specific and less restrictive, Orange said.

A spokesperson for the city attorney's office did not respond to a call for comment.

The lawsuit stems from the arrest of Christian Rodriguez, a teenager living at the time in the Mar Vista Gardens housing project - a stronghold of the Culver City Boys gang.

Rodriguez is neither a member nor an associate of the gang but was placed under the injunction that targets Culver City Boys because of an older brother's ties to the gang, Orange said. LAPD anti-gang officers arrested Rodriguez late one night in June 2009, when they found him outside with friends at the housing project's handball courts. He was charged with violating the injunction's curfew.

The criminal charges against Rodriguez were dropped, but Orange said a broader challenge to the curfews is necessary. Orange said he would try to have the case designated as a class action, which would allow anyone ever arrested for a curfew violation under the 21 gang injunctions to join the lawsuit.