School holidays in Barnsley could change - with the summer break reduced and an extra week added to the October half term.
The proposal is the subject of a public consultation, with people having until December 2 to lodge their views.
Similar proposals, put forward by Barnsley Council, were withdrawn last summer following widespread opposition from parents and teachers.
Nicola Fitzpatrick, of Barnsley's National Union of Teachers, said: “The changing of school holiday dates will create chaos for parents as it could result in parents having their children on holiday at different times depending on whether they attend a council run school or one run by an academy trust.
“Whilst welcoming the consultation it is clearly being rushed through in a matter of weeks and we think the timescale is clearly insufficient for a proper consultation to take place.
“The council claim that they have a wealth of research demonstrating the adverse effects of long summer breaks upon children’s learning, however most existing research in this area relates to the USA where the summer breaks last up to three months. However they have failed to publish this research or demonstrate why shortening the school holidays is in the interests of pupils or their education.”