Norwich City Council used controversial spying powers to investigate and fine a pub for flouting the smoking ban.
Although the name of the pub has not been revealed, the council said that it used Regulation of Investigatory Powers legislation to find out if the pub was allowing customers to smoke in return for a contribution towards any possible fines that may arise.
Formal action was then taken against the pub.
The powers allow councils to access telephone and email records and use surveillance to stop criminal activity.
The information emerged from a Freedom of Information request placed by the Norwich Evening News.
"We only use these powers when absolutely necessary," a council spokesman said.