The California Division of Occupational Safety and Health approved revised workplace guidelines last week that would require workers to continue wearing a mask in some situations even if they are fully vaccinated against COVID-19.

In a marathon hearing that lasted more than six hours Thursday, Cal/OSHA's Occupational Safety and Health Standards Board voted to adopt the revised guidance, which mandates that fully vaccinated workers need to wear a mask if a co-worker in the same room is unvaccinated.

In addition, masks are not required in rooms in which all workers are vaccinated. Outdoors, vaccinated and unvaccinated workers without symptoms only need to wear a mask when working at an event with more than 10,000 attendees.

Employers will also be able to get rid of distancing requirements and protective partitions if they provide N95 respirators to unvaccinated employees.

The board took a circuitous route to approve the revised guidance, voting first against the rules after some business groups argued they're too strict and then voting again to adopt them roughly an hour later.

Those against the revised guidance noted that it is more strict than the guidance for fully vaccinated people issued by the Centers for Disease Control and Prevention, which allows them to forgo a mask in most indoor and outdoor settings if they are more than two weeks past receiving their last vaccine dose.

Board members and business and labor advocates backing the revised rules stressed that they are temporary, only codified until Oct. 2.

The board also said it would work to develop a replacement set of rules. Since last year, all workers have been required to wear a mask at all times, regardless of vaccination status, a rule that would have remained in place had the board voted down the revised rules.

The board also voted to establish a three-member subcommittee to advise Cal/OSHA officials about developing a new set of workplace rules that would likely take effect in August at the earliest.

Most of the rules approved Thursday will take effect June 15 -- the same day the state is expected to remove all capacity restrictions and reopening tiers -- if the state's Office of Administrative Law finds them legally sound in the next 10 days.

Some additional portions of the revised guidance, like the removal of protective partitions and barriers between employees, will take effect July 31.

On Friday, Gov. Gavin Newsom was cagey when asked whether he would issue an executive order by June 15 to override the revised rules, saying only that he felt the board was "moving in the right direction" and that he looked forward to working with business and labor groups to develop future workplace safety guidance.

"We're processing this ... what happened last night just happened last night," Newsom said. "We look forward to updating you more as we make progress towards eventually getting (the pandemic) 100% behind us."