Restaurants and takeaways in Leicester have been given a week to register with the council, or face prosecution.
Environmental health officers have estimated that up to 10% of food businesses may be unregistered.
The move is in response to a number of recent closures due to serious mouse infestations - with half of these being in unregistered premises.
Members of the public are asked to inform city council officers of any businesses operating unprofessionally.
Adrian Russell, service director for community protection said: "While the majority of food businesses in the city comply with food safety legislation, there is a minority who appear to have little regard to food safety matters, and for rat and mouse infestations in particular.
"The message is clear, ensure your business is registered, comply with food safety requirements and take immediate steps to rid your premises or rats and mice."
Anyone who does not register their business in time faces being taken to court.