The council's education and recreation committee decided by 14 votes to 13 that, while teachers should still have two seats on the committee, they would not be allowed to vote.
Alan Findlay, the committee's Liberal Democrat chairman, condemned a decision which he said regarded teachers as "good enough to sit at the table but not good enough to decide anything".
Mr Findlay's 28-strong group runs the council along with six Independent councillors, but it does not hold power since it faces opposition from 23 SNP, seven Tory and four other councillors.
He said he was appalled. "The SNP and Tories obviously don't think that teachers should be directly involved in decisions which affect them. We want to include more people, not fewer, in decision-making. This is a backwards step and a slap in the face for teachers."
David McGinty, Aberdeenshire secretary of the Educational Institute of Scotland, said teachers would be bewildered by the move. "It has never been an issue in the past. This decision is at odds with the inclusive rhetoric of the SNP nationally which does not seem to extend beyond the boundary of the North Esk river."
Jim Davidson, SNP group leader, pointed out that teachers had been the only group of employees allowed a vote.
"We have an education and recreation committee," Mr Davidson said. "It seemed to us inappropriate that teachers should be able to decide on matters affecting libraries or museums or leisure facilities whose staff do not have the same entitlement. There was an inconsistency there, although we are perfectly happy that the teachers' voice continues to be heard on the committee."