Campaigners have started legal action to reverse a decision to reduce the number of children eligible for an autism diagnosis via NHS services.
Sirona, which runs the service in Bristol, North Somerset and South Gloucestershire, said it had to narrow criteria due to a 350% rise in demand.
Assess for Autism has raised £5,000 through a crowd funding campaign to challenge the change.
Sirona said it recognised concerns but said its decision was "clinically-led".
On Thursday, lawyers for Assess for Autism sent Sirona a "letter before action" - the first step of legal proceedings to try to overturn the decision.
Jai Breitnauer, one of the founders of the campaign, has one son with a diagnosis of autism and a second waiting to be assessed.
She said Assess for Autism's campaign had received an "outpouring of support" and had hit its fundraising target in 10 days.
Ms Breitnauer said the campaign was considering launching a judicial re. Send your story ideas to: bristol@bbc.co.uk
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