If it is solely a legal issue that would seem rather petty.
If you want petty then the Wireless Telegraphy Act is the place to find it. I was wondering about the legality of MCW (A2A) transmissions in a band authorised for AM telephony (A3E) and datalink (ACARS) but, as yet, I have not found any definitive requirements on the Ofcom website as to permitted modulation types in the VHF aeronautical mobile band and so have been keeping my powder dry.
Where's Whopity when you need him?