Staff at PC World and Currys are using Facebook to launch a torrent of abuse at customers. Offensive comments have been posted on discussion boards by past and present employees, entitled "Really Stupid Customers!" and "Some customers are really, really stupid".
Despite criticising some customers for being "ignorant", many of the group's 3,000 members have posted comments under their real names.
The shops' parent company, DSG, is understood to be investigating in the wake of the revelations. Posters who said they were employed by DSG said some customers deserved to be punched and one asked if they should be allowed to "cattle prod" others.
DSG said: "We have clear guidelines for staff and will investigate any alleged abuse of customers. Delivering excellent customer service is at the forefront of everything we do, so we are very disappointed a small number of our colleagues have made these comments on a social networking website. We will take the necessary action with any staff found to be acting inappropriately."
British Airways took action last November against staff who complained about customers' "stupid American accents" on Facebook. Virgin was also embarrassed when employees referred to some of the airline's passengers as "chavs".