An unlicensed tattooist operating from a house in Hull has had equipment seized and faces legal action.
Council public protection officers seized the equipment from a house in the Bransholme area of the city.
A spokesman said four people known to have been tattooed at the house were at risk of hepatitis C because of the poor sterilisation methods used there.
He said the council took action after receiving complaints about the business from members of the public.
David Duxbury, the council's head of public protection, said there was "serious concern about the risk of infection being spread between customers".
He added: "People are most strongly advised that if they wish to have a tattoo, they should use only reputable, licensed businesses, where they can be confident that steps will be in place to ensure hygiene and prevent the risk of serious infection being spread."
By law tattooists must register with their local council, who are required to inspect the premises and equipment on a regular basis.