Well, if there is no law against it, it is not illegal.
I'm not a lawyer, but here is a quote from my lawyer in Thailand:
In my home country of America, the fundamental basis of law is that every act is LEGAL, unless there is a law that makes that act illegal. Thailands fundamental basis of law is quite different in Thailand, every act is ILLEGAL, unless there is a law (and process, and procedure) to make it legal.