Code of Federal Regulation help

I am looking for the rule that says Providers must bill all carriers if billing for one carrier. When a carrier has a specific item they have decided they are going to pay for and gives you the HCPCS/CPT codes to bill to them, like Cigna who now pays the afterhours or disruption of office schedule codes, do we have to bill ALL carriers when we know only one Carrier is going to reimburse?
I understand that if we charge for a procedure we should charge the same amount to all carriers. My question is do we HAVE to bill all carriers when one carrier deicdes to pay for something that no one else does?

Thank You

I have no reference

but Federal Regulations only govern Medicare/Medicaid. So no one but your contract will tell you what to do for each insurer.
That being said, teaching docs to bill differently for different insurers is nearly impossible (unless you are teaching me) so sometimes it is better to bill all and write off those that do not pay. It also allows the charge to show up on the patient's EOB and see the insurer pay nothing and you get sympathy from the patient (at least in a perfect world where patients actually care about their bills and actually pay them.)