The government want early primary classes to have 18 pupils
Teachers have once again demanded government action over class sizes.
Members of Scotland's largest teachers' union, the EIS, will decide at their annual conference whether to have a vote on industrial action.
The union's leader has called for legislation to reduce pupil numbers but councils have said schools cannot be shielded from pressure on public funds.
Government policy is to have early primary classes limited to no more than 18 pupils.
According to Ronnie Smith, general secretary of the EIS, almost half Scotland's councils have made no progress at all in reaching this target.
He said: "It is time now for the Government to bite the bullet and move to promote regulations to limit class sizes across all our schools.
"I know it is difficult to secure legislation as a minority administration.
"But all MSPs, of all parties, should be challenged to vote against legislating to cut class size - to vote down the chance to deliver on the promises they nearly all made at the last election."
He added: "The local authorities have had their chance and too many have failed to make progress - some of them quite consciously and deliberately."
Some 14 councils have made "no progress whatsoever" on cutting class sizes, he said.
He said the issue raised a bigger question abut the relationship between central and local government in education, and warned that EIS support for the central role of councils is not unconditional.
"If nationally, parties make manifesto promises they must have the tools, the means of securing delivery," said Mr Smith.
"They cannot hide behind soft, touchy-feely understandings with councils or periodic bi-lateral chats and visitations.
"It is clear that some councils see themselves as bigger than the Government when it comes to running schools and determining education policy and are determined to plough their own furrow."