The union said silent transmissions may be happening all over Hong Kong, and the Education Bureau should extend class suspension for kindergartens, primary and secondary schools until this wave of outbreaks subside.
They face-to-face classes are suspended until late February.
The union urged authorities to postpone the Diploma of Secondary Education Examination (DSE), cancel the internal assessment for secondary school placement and cancel part of the Territory-wide System Assessment (TSA) for primary six pupils.
The union said authorities should make public any decisions as soon as possible, so schools and pupils have time to make preparations.