At least three police unions in Contra Costa County have asked a court to block public access to officer misconduct records for incidents occurring before 2019, arguing that California’s new police transparency law did not specifically address retroactivity.

Police associations in Concord, Antioch and Richmond have each sued their respective cities and police chiefs in Contra Costa County Superior Court, arguing against the release of records. The filings come amid a flood of public records requests prompted by the law that took effect Jan. 1.

Law enforcement unions in Orange, Ventura, Los Angeles and San Bernardino counties have filed similar suits.

SB 1421, authored by state Sen. Nancy Skinner, is intended to shed light on police disciplinary records that for years have been protected by some of the most stringent privacy laws in the country, according to the measure’s supporters. The law opens certain misconduct records pertaining to sustained findings of sexual assault or dishonesty on the job, and for investigations involving an officer’s use of a firearm or other use of deadly force.

Police transparency advocates say there is no ambiguity in the law and that its intent was clearly aimed to unseal all applicable records currently maintained by police departments. This, they say, includes records of conduct for incidents from previous years.

“This is a coordinated effort by police unions to undermine a law that was overwhelmingly supported by organizations and individuals throughout California,” said Melanie Ochoa, an attorney with the American Civil Liberties Union of Southern California. “(It) was enacted by legislators to ensure that the public finally had some insight into police misconduct.”

Ochoa said ACLU attorneys will be arguing against the unions in court. The ACLU is currently seeking records for several high-profile police shootings, including the killing of Oscar Grant at an Oakland BART station a decade years ago.

A hearing on the Contra Costa County suits is scheduled for Friday at 10 a.m. in Contra Costa Superior Court in Martinez.

In their court filings, union attorneys said the law in place prior to SB 1421 “afforded peace officers a confidentiality privilege to all the information contained in their personnel files.”

“SB 1421’s changes, therefore, must operate prospectively only,” the attorneys argued.

The unions also asked the judge to issue a restraining order that would prevent the departments from disclosing the records before the court makes a final decision.

San Bernardino County Sheriff’s Employees’ Benefit Association already filed a similar suit with the California Supreme Court, but the high court declined to weigh in on the matter, according to the Desert Sun.

The Chronicle, along with several other media organizations and advocacy groups, filed public records requests to various police departments and sheriff’s offices at the start of the New Year. California public records law requires agencies to respond to the request in 10 days, but most departments to date have asked for extensions.

Joseph R. Lucia, an attorney for all three police unions, emailed copies of the suits to The Chronicle and other organizations on Thursday. Lucia said none of the cities are expected to oppose a temporary restraining order, but are expected to oppose the underlying petition.

Attorneys for the unions did not respond to requests for comment.

Megan Cassidy is a San Francisco Chronicle staff writer. Email: megan.cassidy@sfchronicle.com Twitter: @meganrcassidy