It's happening at three locations including the San Francisco Hall of Justice, the Civic Center Courthouse, and the Juvenile Justice Center.
Courtroom clerks on the picket line are calling for more staffing and better training.
In the San Francisco Superior Court system, courtroom clerks are often the glue holding the justice system together, with judges depending on their work.
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"We're the fact checkers, we are the last line of defense to make sure all the T's are crossed, all the I's are dotted and that oversights don't happen," Ben Thompson, a deputy courtroom clerk said.
Angelica Young has been a deputy courtroom clerk for 26 years.
"We're just drowning, we've literally been treading water," Young said.
She says, staffing, technology and training issues are leading to a massive backlog in the courts, delaying both civil and criminal cases and causing more than 70 misdemeanor cases to be thrown out.
"We want to just be at the table and have them understand and give us what we need to do our job, training, staffing, technology that is actually efficient," she said.
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As far as impacts, courts are staying open with the help of management employees.
"It is unfortunate that SEIU has decided to disrupt court services after our many hours of negotiations, and a mediation session, to reach a fair contract that reflects the economic impacts from the state's reduction in funding," Brandon Riley, Executive Officer of the San Francisco Superior Court said.
Riley said the state cut the court's budget by $2.5 million this fiscal year.
"An institution like this that doesn't bother training its employees and that obviously doesn't care if they are serving the public which I think is one of the cornerstones of our criminal justice system, to not care about that, is ridiculous and embarrassing," Thompson said.
Although union leaders say this is only planned to be a one-day strike, if court management doesn't get the message, they say they're ready to walk again.
"If they don't want to budge honestly, we can shut this down because not to put too fine of a point on it, if there aren't clerks in your courtroom and there aren't court reporters in your courtroom, you don't have a courtroom," he said.
This action is impacting the high-profile murder trial of Cash app Founder Bob Lee as the court reporter for that case joined clerks outside on the picket line.
ABC7 reporter Melanie Woodrow, who has been covering that murder trial, says all attorneys went home early.
San Francisco District Attorney Brooke Jenkins sent ABC7 News a statement supporting the clerks and saying that managers need to bargain in good faith:
"Court clerks play a critical role in ensuring that operations at the Hall of Justice and the other court houses in the city function smoothly to ensure justice for victims of crime and the fair and impartial administration of the criminal justice system for those accused of crimes. Courthouse managers need to come back to the table as soon as possible and negotiate in good faith with the clerks. Ensuring that we have appropriate staffing levels and access to training and resources for the clerks is fundamental to a well functioning justice system."