PHILADELPHIA (CBS) — A new fight is brewing just days before Philadelphia teachers are supposed to return to school. The Philadelphia School District expects pre-kindergarten through second-grade teachers to show up at school on Monday to get ready to welcome students back.

The students who chose hybrid learning are scheduled to return to the classroom two weeks later on Feb. 22, but new safety concerns from the Philadelphia Federation of Teachers is throwing that schedule in the air.

READ MORE: District Attorney Larry Krasner, Mayor Jim Kenney Speak Out On Philadelphia's Ongoing Gun Violence Crisis

As many as 2,000 teachers are expected to return to classrooms in Philadelphia on Monday, to prepare for in-person learning for pre-kindergarten through second-grade students.

The school district has spent $4 million upgrading ventilation systems in buildings, adding fans and checking room temperatures to try to mitigate the spread of COVID-19.

“We put those fans in and used the size of those fans, was so that we would not create conditions that were too cold for young people, and that’s why we went with the smaller type of device,” Philadelphia School District Superintendent Dr. William Hite said.

District officials say this is a temporary solution to ensure that students and staff can all return to schools safely on Feb. 22.

“Every classroom has to have adequate ventilation,” Philadelphia Federation of Teachers President Jerry Jordan said.

Jordan isn’t convinced that buildings are safe enough for teachers and students to return and he’s calling for a third-party to intervene.

READ MORE: New Jersey Mother, Danielle Mead, Four Children Safely Located, Gloucester Township Police Department Says

“We don’t believe that the classrooms are safe for all of the staff and students to return and the district believes that it is. Well, we have a third-party — neutral — who’s going to hear from both sides and will make a decision,” Jordan said.

With the deadline for the start of hybrid learning looming, Hite says he has no plans of delaying a return to classrooms.

“We don’t have a thought of prolonging it and we’re moving forward. I think, as I’ve said before, safety and choice are the two pillars on which these plans were created,” Hite said. “Families still have a choice. They can choose not to send their young people back and keep them in a virtual environment, if, in fact, they are concerned, and that has always been the case.”

According to the teachers’ union, the third-party would be someone who is an expert on ventilation, airflow in buildings and COVID-19. Jordan says this will be happening throughout the weekend and will have more on what happens next on Sunday.

MORE FROM CBSPHILLY.COM

EXCLUSIVE: Lawsuit Alleges Ridley Township Top Cop Scott Willoughby Conspired With Elected Township Officials In Interfering With FBI Investigation

COVID In Delaware: Restaurants, Gyms, And Other Businesses To Operate At 50% Capacity Beginning Feb. 12

MORE NEWS: Teenager Killed In Trenton Shooting Identified As Shemiah Davis, Mercer County Prosecutor's Office Says

Chalfont Borough Residents Asked To Shelter-In-Place Due To Ongoing Police Activity