In the US, if a civil aircraft has a UHF radio are there any regulations against it performing ATC communication on the UHF bands?

Pointers to the appropriate CFR's would be appreciated.

This question does not concern operating under an emergency state of any kind. The aircraft is assumed to be in compliance with all regulations otherwise at the time.

The reason for excluding emergency status, is that in an emergency the FCC states you can use whatever methods available to obtain help.