Strathclyde Police has entered an agreement with US retail giant Wal-Mart over a portable unit at an Asda store in the north of Glasgow. The supermarket, in Robroyston, was the scene of the murder last year of gangster Kevin "Gerbil" Carroll.
An Asda spokeswoman said: "We hope customers and colleagues will benefit from having access to officers."
However, unions representing police civilian staff and members of Strathclyde Police's governing body have raised ideological and practical concerns, including over preferential policing and the impact on other stations.
Stevie Diamond, chairman of Unison's Strathclyde branch, said: "What's the impact if Asda decides to the pull the plug?"
The office plan resulted from a "positive relationship" police had built with Asda and Wal-Mart after Carroll's murder in January last year. The incident led to the firm having "a detrimental effect in terms of its customer base".
Under the deal, police will pay £50 a month in rent, with officers onsite for at least 25 hours a month. A Strathclyde Police spokeswoman said: "Asda aren't paying any costs towards policing."
Meanwhile, Scottish police are to be spared cuts to pay and conditions planned for their counterparts south of the Border, Ministers have decided.
Justice Secretary Kenny MacAskill gave the news at a conference on creating a single police force as he attempts to win support for the move among a sceptical rank and file.