Do you need an actual licensed plumber to install a shower pan in a stand alone shower?

I have part of my bathroom and shower being redone and retiled because of water damage to the shower, and into the closet next to it. It is recessed about 4". Some contractors have said they would install a shower pan which we did not have- just concrete and tile. The contractor we are using was going to put 1 in, but says we don't need one. He says that if it is put in, that a licensed plumber has to do it. Do we need a shower pan and does it have to be done by a licensed plumber? Can you help w these question? I am in Florida