Two Phoenix-area school districts have shifted their mask policies as students return to classes Tuesday after winter break.

On Monday, the Scottsdale Unified School District announced that it’s requiring masks for all staff indoors in an effort to preserve the district’s ability to offer in-person instruction. However, masks will be strongly recommended for students. The district had required masks for both students and staff prior to the winter break. Volunteers and visitors will not be allowed on SUSD campuses until further notice, the district said in its statement. SUSD will also limit assemblies and large, indoor gatherings during school hours.

→ List: Arizona school districts requiring masks for 2021-2022 school year

The district is monitoring COVID-19 cases at each school site, and may take stronger mitigation measures, including requiring masks, if it sees evidence of in-school spread of the virus.

Meanwhile, Glendale Union High School District announced Monday that it's requiring masks for all students, staff and visitors for the first time this school year citing a surge of COVID cases due the omicron variant.

"In order to help keep our students, staff, and community healthy and to make every effort to have our schools remain open for in-person learning, we need to implement another level of mitigation," GUDSD said in a statement. 

The Glendale district will monitor COVID-19 cases and the advice of health experts to evaluate the mask requirement on a regular basis. The first review will take place no later than Jan. 28, it said. 

Over the weekend, the Kyrene School District in the East Valley announced that it reversed its decision to make masks optional after the winter break.