The reminder comes after fashion retailer Internacionale was fined £2,000 when staff at its Carlisle store were found to be working at 7.6°C well below the legal minimum. There was no central heating in the store and the doors were wide open all day.
According to the Workplace Health and Safety Regulations 1992, the temperature during working hours in all workplaces inside buildings should be "reasonable" and measure at least 16°C.
Doug Russell, health and safety officer for shopworkers' union Usdaw, said that convenience stores in particular should take note of the warning.
"Convenience stores often leave their doors open to attract passing trade, which is perfectly acceptable as long as they ensure that inside temperatures reach the legal minimum of 16°C.
"Forcing staff to work in cold temperatures is also bad for business as cold staff will be less productive, and could potentially become ill."