Philadelphia will be reimposing its city-wide indoor mask mandate amid an uptick in cases of COVID-19’s omicron BA.2 subvariant, officials announced on Monday.

The mandate will go into effect next Monday, and requires masks inside “schools and childcare settings, businesses, restaurants, and government buildings,” the Philadelphia Department of Public Health said in a statement on social media.

“At that time, residents will be asked to report any business not complying with the mandate to @philly311” the department added.

Philadelphia will become the first major city to reinstate the indoor mask mandate after most state and local governments lifted restrictions after coronavirus cases plummeted following a surge in the winter.

According to PDH data, as of April 11 the city is averaging 142 new cases per day and 44 hospitalizations — a 50 percent increase from the previous 10 days. The increase triggered the city to activate the level 2 COVID-19 response system, which includes requiring masks indoors.

The mandate goes against current CDC guidelines, which lists Philadelphia County’s current COVID-19 transmission level as “low.” Under the low-level guidelines, masks are optional but recommended for those with symptoms, a positive test, or who have been exposed.

“Our city remains open; we can still go about our daily lives and visit the people and places we love while masking in indoor public spaces,” Philadelphia Mayor Jim Kenney tweeted Monday. 

Nationally, the 7-day average for new COVID-19 cases has hovered around 26,000 since mid-March after dropping sharply from an all-time high of 806,739 on January 15, according to CDC data.