A council has confirmed it is investigating a complaint from a neighbour about a couple smoking in their own home.
A woman, who has not been named, has written to the council saying cigarette smoke from next door was "permeating into her living room".
Gwynedd Council's public protection service has said it has a duty to investigate.
Gavin Gordon-Crawley, the subject of the complaint, called it "a joke".
Mr Gordon-Crawley, 51, who smokes 20 cigarettes a day and whose wife is a social smoker, told The Sun newspaper: "I can understand smoking bans in certain places - even a total public smoking ban.
"But being told I can't smoke in my own home. It must be some sort of joke."
The complainant says smoke is 'permeating into her living room'
Jeanette Gordon-Crawley, 54, who lives in a semi-detached house, added: "We can't see how smoke from our house could possibly get into the house next door.
"People have a right to complain if you smoke near them, but we have the right to the occasional cig in our own home."
A spokesperson for Gwynedd Council said it had a "statutory responsibility" to investigate the neighbour's complaint.
"The person complaining alleges that smoke from a neighbouring property is able to enter their property.
"What people do within their own homes is of no concern to us, as long as they do not affect other people," the spokesperson added.
"In this instance, we have received a complaint stating that smoking in a house in the Caernarfon area is causing a nuisance to the neighbours and as a local authority we have a statutory responsibility to investigate this complaint.