Leaked internal documents show that the insurance giant is culling providers of applied behavior analysis from its network and scrutinizing the medical necessity of therapy. Advocates say the company’s strategy may be illegal.

ProPublica has obtained what is effectively the company’s strategic playbook, developed by Optum, the division that manages mental health benefits for United. In internal reports, the company acknowledges that the therapy, called applied behavior analysis, is the “evidence-based gold standard treatment for those with medically necessary needs.” But the company’s costs have climbed as the number of children diagnosed with autism has ballooned; experts say greater awareness and improved screening have contributed to a fourfold increase in the past two decades — from 1 in 150 to 1 in 36.

So Optum is “pursuing market-specific action plans” to limit children’s access to the treatment, the reports said.

“Key opportunities” are outlined in bullets in the documents. While acknowledging some areas have “very long waitlists” for the therapy, the company said it aims to “prevent new providers from joining the network” and “terminate” existing ones, including “cost outliers.” If an insurer drops a provider from its network, patients may have to find a new clinician that accepts their insurance or pay up to tens of thousands of dollars a year out of pocket for the therapy. The company has calculated that, in some states, this reduction could impact more than two-fifths of its ABA therapy provider groups in network and up to 19% of its patients in therapy.