A group of protesters who say advertising on Melbourne's public transport network is undemocratic, are tearing down ads while posing as authorised workers.

Dressed in official-looking hi-vis vests, members of a group calling itself "Tram Clean" have removed dozens of posters from tram stops around the city in what they are calling a "theatrical protest".

Images began circulating on Tuesday of stickers at tram stops left in the place of several missing posters.

"This ad has been deemed destructive and has been removed," it reads, along with a link to the group's website.