You are correct!
Junk fax (spam) is unwanted fax that people don’t ask for. One problem with junk fax has is that the sender ties up the phone lines and the uses the recipient’s paper. Because of all of these problems, there is now a law called The Telephone Consumer Protection Act (47 USC 227), or the TCPA. This law outlaws certain practices including the transmission of junk fax. The only exception is when the recipient gives the sender permission for the advertisement.