In a written policy statement, the union's Scottish executive committee has endorsed the government's target of a maximum of 18 pupils in P1-P3 classes.
The statement said: "Voice urges that, once this is established, a further aim should be to extend this maximum year-on-year as these cohorts progress through primary school."
In secondary schools the union wants class sizes kept to a maximum of 20 in English and maths.
"Voice recognises there will be implications for staffing resources and costs," the statement said. "Over the past few years there has been increased investment in training more teachers. Drawing on this resource, coupled with the general trend towards falling pupil rolls, there is an opportunity to start reducing class sizes."
News
Scottish union calls for smaller class sizes
Education union Voice has demanded the Scottish government work towards smaller class sizes.
