The Los Angeles Unified School District said it will prohibit students from wearing cloth masks due to the spread of the COVID-19 variant, omicron.

Starting Monday, students must wear “well-fitted, non-cloth masks with a nose wire” at all times, including outdoors, the district announced.

Higher grade masks will be made available to students upon request, the announcement added.

The shift away from cloth masks was prompted by guidance from Los Angeles County health authorities, said Shannon Haber, a spokeswoman for LAUSD.

LAUSD, the nation’s second-largest school district, does allow exemptions to mask rules for some students who have a disability, medical or mental health condition that makes them unable to comply, the Los Angeles Times reported.

Health officials in Los Angeles and across the state have increasingly urged all residents to upgrade masks to surgical-grade or greater, such as N95 and KN95 masks, to protect against the omicron variant.