Three Florida school districts have filed a legal challenge against the state health department, seeking to invalidate an emergency rule that allows parents to opt out of mask mandates.

The petition, filed Friday, argues that the emergency rule -- issued after Gov. Ron DeSantis ordered the health department to protect parents' choice when it comes to masking their children -- exceeds its authority and is invalid.

The school districts in Alachua, Broward and Orange counties, which all require students and staff to wear masks, requested that an administrative judge hear the case.

Florida's education commissioner has withheld the salaries of school board members in Alachua and Broward counties over their mask mandates -- and has threatened similar action in Orange County.

Last week, a Tallahassee judge ruled in favor of a group of parents who sued the state over its ban on mask mandates. That ruling is being appealed.

-ABC News' Will McDuffie

Over 2.1 million people were screened at U.S. airport security check points Friday -- the highest checkpoint volume since Aug. 15, Transportation Security Administration spokesperson Lisa Farbstein said. 

Americans have flocked to airports to travel for the Labor Day weekend despite the threat of the delta variant and surging COVID-19 cases and hospitalizations. 

The U.S.’ daily case average remains around 153,000 cases a day, up by approximately 964% in the last two months. 

Overnight Friday, the U.S. recorded its second single-highest day of COVID cases this week with more than 170,000 new cases reported.

Every state in the country is currently experiencing high community transmission. The South still leads the country with the highest case rates. Tennessee, and South Carolina currently have the country's highest case rate, followed by Mississippi, Florida, Georgia and Wyoming, all with case rates above 600 per 100,000 people.

-ABC News' Ahmad Hemingway and Arielle Mitropoulos

This year’s Made In America festival over Labor Day weekend in Philadelphia will go on with COVID-19 restrictions.

Despite surging delta variant cases and flooding from the Schuylkill River that inundated the Ben Franklin Parkway with water, the festival will continue, officials said. 

"I think it's good for the city to have this kind of event, so we can celebrate a little bit even in the midst of potential tragedy. Jay-Z, Beyonce, the Biebs (Justin Bieber) is coming," Philadelphia Mayor Jim Kenney said Friday. “It'll be fun for a change...be nice to have some fun, wouldn't it?"

Roc Nation, which is producing the two-day festival, said all attendees will need to wear masks. Attendees will also have to show proof of a negative COVID-19 test or printed proof of full COVID-19 vaccination to get in. 

"The negative COVID-19 test result must be obtained within 48 hours of attending the Made In America festival," said Roc Nation on the festival’s website. 

Philadelphia officials also updated the city’s mask mandate in August to require masks at all non-seated outdoor events with over 1,000 attendees.

Jacqueline L. Jackson, the wife of civil rights leader Rev. Jesse Jackson Sr, has been released from the hospital after receiving treatment for COVID-19, her family said Friday. 

"Our mother is leaving the Northwestern Memorial Hospital and coming home," the family said in a statement. "Our family is grateful to God and the medical team that treated her and that is allowing her body to continue to heal from the COVID-19 virus."

She had been in the ICU after testing positive for the virus. Jacqueline, 77, was not vaccinated. 

Her husband Rev. Jesse Jackson, 79, remains at The Shirley Ryan Ability Lab where he’s receiving intensive occupational and physical therapy. He has Parkinson's disease and was vaccinated, ABC Chicago station WLS reported.

"We urge all who have not yet been vaccinated for the COVID-19 virus to do so immediately,” the family said in a statement. 

The family had announced the couple was hospitalized with COVID-19 on Aug. 21.