Health minister Mark Drakeford revealed a list of places where the ban would apply at a meeting of the assembly's health and social care committee, arguing that vaping would be treated differently to smoking and would only be banned in certain places.
Vaping would be allowed in wet-led pubs that don't serve food and where unaccompanied children are banned.
Welsh Liberal Democrat Kirsty Williams added: "I have concerns about the approach the Welsh government has taken. I am not convinced that the measures proposed (to stop vaping) will enhance the health of people in Wales, or are proportional. By persuading people who smoke to use these devices, we could prevent a number of premature deaths."
Williams also accused the legislation of being "unclear" on where people would be able to vape.
Assembly member Darren Millar added: "Many wet-led pubs serve pickled eggs, pork scratching and packets of crisps on the bar. Are these pubs included in the ban or not?
"I have to say I am yet to find a single pub that doesn't have some element of people being able to munch their way through some sort of snack while they enjoy a pint or any other sort of drink."