Members of Scotland's largest teaching union, the EIS, have voted for a ballot on taking action in pursuit of classes with no more than 20 pupils.

A majority also called for the cap to have statutory force.

The union's leader has claimed almost half of Scotland's councils have made no progress towards the government target of 18 pupils per class.

A union spokesman said: "This clearly indicates that Scottish teachers feel let down on class sizes.

It is time now for the government to bite the bullet and move to promote regulations to limit class sizes across all our schools Ronnie Smith, EIS

"Promises have been made to reduce class sizes in our schools, and the progress has been extremely limited to date.

"Some local authorities have openly refused to work towards their commitments to reduce class sizes, in defiance of the Scottish Government's stated aims and the concordat that local authorities freely entered into.

"The message to the Scottish Government and local authorities is clear - teachers expect the promises made to them on class sizes to be kept, and teachers will do everything possible to hold our political leaders to account."