The lawsuit, filed in Commonwealth Court on Saturday, said Philadelphia lacks the authority to impose such a mandate.

Philadelphia earlier this week became the first major U.S. city to reinstate its indoor mask mandate after reporting a sharp increase in coronavirus infections, with the city’s top health official saying she wanted to forestall a potential new wave driven by an omicron subvariant.

Attorney Thomas W. King III, who was among those involved in last year’s successful challenge to the statewide mask mandate in schools, said the city’s emergency order went against recommendations of the federal Centers for Disease Control and Prevention and “imposed a renegade standard unfound anywhere else in the world.”

The suit accuses city health officials of having “usurped the power and authority” of state lawmakers, the state department of health and the state advisory health board.

Kevin Lessard, communications director of the Philadelphia mayor’s office, said officials were “unable to comment on this particular case” but cited a court’s denial of an emergency motion by another plaintiff for a preliminary injunction against the mandate. Lessard said “the courts once again confirmed that city has both the legal authority and requisite flexibility to enact the precautionary measures necessary to control the spread of COVID-19.”

Most states and cities dropped their masking requirements in February and early March following new guidelines from the CDC that put less focus on case counts and more on hospital capacity and said most Americans could safely take off their masks.

Philadelphia had ended its indoor mask mandate March 2. But on Monday Dr. Cheryl Bettigole, the health commissioner, cited a more than 50% rise in confirmed COVID-19 cases in 10 days, the threshold at which the city’s guidelines call for people to wear masks indoors.

“If we fail to act now, knowing that every previous wave of infections has been followed by a wave of hospitalizations, and then a wave of deaths, it will be too late for many of our residents,” Bettigole said. Health inspectors are to begin enforcing the mask mandate at city businesses on Monday.

The restaurant industry pushed back against the renewed mandate, saying workers will bear the brunt of customer anger over the new rules.

The state Supreme Court in December ruled that the governor’s administration had no legal authority to require masks in Pennsylvania’s schools and child care centers, citing state lawmakers’ elimination of an emergency disaster declaration. The 6-0 ruling said state law gives health officials broad authority to protect public health but doesn’t permit the department “to act by whim or fiat in all matters concerning disease.”