It's the state practice act and scope of practice. Internal policy of a facility can also dictate this. In addition, some payers may have regulations regarding requiring a "written order" or referral from the referring provider. WC probably won't allow it without auth for example.
However, most states (if not all) now have direct access. The therapists can most certainly see a patient for an Initial Evaluation without an order, but the payer may not want to pay for it. Depends.
This is a question for your supervisor, manager, or internal compliance department. As a staff coder, you should not be determining or making a decision on this (my opinion). You are questioning their clinical practice and scope of practice. This is what they do on the initial eval or re-eval. If it is outside of their scope, they would refer the patient to an appropriate provider. For example, I can make an appointment independently, walk into my local outpatient PT for my eval and they can either create my plan of care and set up my treatment, or refer me to another provider. Maybe I need an MRI, CT, X-Ray, etc. There are practices that do not accept patients without a referral or order from their PCP or MD, DO, PA, NP, etc. but that is an internal policy or maybe they are heavy WC or Medicare. An HMO may require a patient to have a referral/order.
Here is an example UHC policy (not CO though):
https://www.uhcprovider.com/content...p/rehabilitation-services-pt-ot-st-common.pdf
"Services must relate directly and specifically to a
written treatment plan established by a physician after consulting with the qualified therapist (Physical and/or Occupational) and/or speech pathologist or audiologist.
You can also check CMS/Medicare regulations.