Ontario's school principals say they are concerned about the impact the province's changes to autism service delivery will have on students.

In a joint letter to Education Minister Lisa Thompson, three principals' associations say the changes announced last month will mean many students will be spending less time in therapy with trained professionals.

The groups say those students will now spend more time in school and, with current funding levels, their additional learning, safety and behavioural needs won't be met.

They also warn that most school staff do not have the required medical and professional training to treat, teach or manage children with autism.

The principals say that if the necessary resources aren't made available to schools by April 1, the government should delay the program changes.

Thompson says she has a good working relationship with the province's educators and the government is moving forward in a way meant to ensure all voices are heard regarding the autism program changes.