The Local Government Association, which represents councils in England, said the pressure had ramped up over the past three years.
“Continuing to fulfil the current statutory responsibilities for home to school transport is becoming increasingly financially unsustainable, posing a real threat of bankruptcy for some, and necessitating cuts to other vital aspects of children’s services provision in many more,” it said in a report this summer.
Rob Williams, senior policy advisor at school leaders’ union the NAHT, said funded transport “plays a crucial role” in helping many children “attend school regularly and develop their independence”.
“However, a growing number of councils are reducing transport provision due to increasing budgetary pressures, and when children simply cannot get to school this threatens to deepen existing attainment gaps and place even more pressure on already stretched parents,” he added.
Ministers have faced calls not to cut education, health and care plans (EHCPs) for children and young people with Send.
Last month, the education committee recommended that the government keep them.
The National Audit Office has previously said the Send system in England is “broken”, not financially sustainable and failing to deliver better outcomes for children and young people.
Cllr Bill Revans, Send spokesperson for the County Councils Network, said the current system “does not work for young people, families and councils alike”.
The DfE announced last week that it was delaying reforms to the Send system and other policy proposals for schools in England until next year.
Education Secretary Bridget Phillipson said there would be a “further period of co-creation, testing our proposals with the people who matter most in this reform”.
Cllr Revans said that delay was “massively disappointing”, but that it was vital the government used the time to “set out genuine root and branch reform to the system”.
School Standards Minister Georgia Gould said the schools white paper would “ensure more children can have their needs met in their local school”.
She said work had already begun to improve the system, and added: “My message to families is that it won’t stop here. We’re absolutely determined to deliver a better system that supports your children at every stage.
“Over the next few months, I’ll be meeting with more parents across the country to make sure your experiences are at the very heart of our reforms.”
Additional reporting by Wesley Stephenson.