A landmark attempt to open up records of police use of force and misconduct in California has turned into a broad legal battle as law enforcement unions across the state have gone to court to stop the release of some of the documents.

An Orange County judge on Thursday issued a temporary restraining order to block the Sheriff’s Department from disclosing records from incidents that took place before Jan. 1, when the transparency law went into effect.

Like other unions, the Assn. of Orange County Deputy Sheriffs argued that applying Senate Bill 1421 retroactively would violate long-standing legal protections for officer personnel files.

“To have the rug pulled out from under them isn’t fair,” Jacob Kalinski, an attorney for the AOCDS, said after a hearing on the request. He noted his request is meant to pause any release of records so the legal issues involved can be examined more closely.

Laura Knapp, an attorney for Orange County, opposed the union’s move, arguing that the new law applies to documents currently in the county’s possession, which includes records of incidents before Jan. 1.

“We are committed to transparency,” she told Superior Court Judge Nathan Scott at the hearing.

The Times, along with Voice of OC and Southern California Public Radio, applied to intervene in the case in favor of disclosure.

In Los Angeles County, open-government advocates and media organizations, including The Times, filed court papers Thursday asking for permission to challenge a temporary order blocking the city of Los Angeles and the Los Angeles Police Department from releasing the same kind of records. The order was requested by the union that represents LAPD officers.

The unions representing deputy sheriffs in Los Angeles County and Ventura County have each filed their own requests to block disclosure of records of incidents prior to Jan. 1. A judge in San Bernardino County granted a similar request from a local law enforcement union.

Until last year, the state’s powerful law enforcement unions repeatedly blocked attempts to make any disciplinary records public. But lawmakers approved SB 1421 amid a heightened debate over how officers use force and interact with communities of color.

The law covers records of shootings by officers, severe uses of force and confirmed cases of sexual assault and lying by officers. Proponents of the measure say restricting its reach to records of incidents after Jan. 1 severely limits the law’s impact and shields misconduct by some officers who remain on the job.

“Officers have been escaping responsibility for their past acts,” said Melanie Ochoa, an attorney with the American Civil Liberties Union of Southern California, which backs disclosure and filed to intervene in the lawsuit brought by the union representing LAPD officers.

Ochoa said there have been records released under the new law that show a pattern of misconduct that could otherwise have remained hidden. In San Mateo County, the district attorney said he would consider reopening a criminal investigation into an officer accused of an attempted sexual assault after records surfaced showing the officer had a history of similar allegations. “There is a pressing, current need to make sure officers are not engaged in very egregious acts of misconduct and to understand how police departments are evaluating use of deadly force,” Ochoa said.

Scott Tiedemann, an attorney who represents police managers across California, said many of the unions appear to be concerned that records created with an expectation that they would be kept private will now be subject to disclosure. He said police agencies do not have the funding to respond to voluminous requests for records that date back decades. He said a more reasonable solution would be for the law to be interpreted to apply to records as far back as five years.

“There are many good things that can happen as a result of the increased transparency,” said Tiedemann, a managing partner of Liebert Cassidy Whitmore. “But right now, public resources are being spent on disclosing old records for incidents where the people don’t necessarily work at those departments anymore and the incidents ... don’t necessarily reflect the practices of the agencies now.”

Sen. Nancy Skinner (D-Berkeley), who wrote the law, said her intent was for it to apply to any records in a department’s possession. But she said if a court decided otherwise, the rules could still provide a needed boost to transparency surrounding police activities.