The EIS has raised concerns at plans by Dumfries and Galloway Council to raise the maximum number of pupils in single teacher schools from 19 to 25.
The proposal has sparked fears that a number of smaller rural schools may become unviable and subsequently face closure.
Commenting on the plans, local EIS secretary Andrew O’Halloran said: “These plans undermine rural schools. The level of responsibility for one member of staff potentially having to teach all seven primary classes simultaneously is enormous.
“The danger is that parents may choose to send their children elsewhere, making some rural schools unviable. This is nothing short of school closures through the back door.”
The EIS is currently engaging with parent groups to work to reverse these changes.
Mr O’Halloran continued: “It is feared that posts in single teacher schools will become much harder to fill. There are also concerns that these moves will eventually have an impact on less well-off families in rural areas.
“The union contends that the budget set by the council runs a coach and horses through the Scottish Governments’ closing the poverty gap agenda. SNP members in the administration are thwarting their own party’s policies.”
EIS Equalities representative Sarajane Moffat, added: “If smaller schools are undermined in this way and are forced to close their doors then those on lower incomes will face much higher costs. The answer is to keep pupil numbers in single teacher schools at 19.”