Government plans to give schools more freedom over the pupils they admit are being opposed by Derbyshire County Council.
The moves would allow an infant school to become a primary or allow a school to expand its intake without seeking the permission of the local authority.
Councillors believe such powers could lead to a lack of school places being available in the future.
Cabinet member for children Coun Kevin Gillott said: “I have serious concerns about these proposals.
“It could mean the council is unable to fulfil its statutory duty to ensure there are enough school places available to all children.
“Without money to expand, a school changing its age range may have to reduce the places available in each year group.
“This, and their ability to change the number on roll without our permission, could lead to a severe shortage.
“This kind of wholesale change needs to be well planned to ensure all children get the education they deserve. It may also cost taxpayers more money as we’re forced to adapt our services because of the actions of individual schools.”