Highlands public school teachers will stop work on Thursday.
They will vote on a proposed industrial agreement covering salaries and conditions with the NSW Department of Education.
As a result of this, there will be minimal supervision at schools until classes commence by 10.30am.
It is understood schools that have planned an event such as a concert or picnic will be exempt from this arrangement.
A NSW Department of Education spokesman said schools would operate as normal on Thursday.
"All students will be supervised during the NSW Teacher's Federation meeting," the spokesman said.