The Department of Work and Pensions, one of Whitehall's biggest adspenders, with an annual budget of around £20 million, wants a more direct relationship with agencies on some campaigns.
Its call mirrors a similar request by the Home Office, which is in talks with COI bosses about taking a more hands-on role.
Simon MacDowall, the director of communications at DWP, said: "COI offers a good service in a number of areas. But it would be nice to choose from a range of options depending on the expertise we have in the department and what we want to buy in."
Officials at DWP and the Home Office insist they are not trying to break away from COI and will continue to use its roster.
COI chiefs are happy to offer Whitehall clients a more tailored approach but want to head off potential contractual problems. Because agency contracts are with COI rather than individual departments, COI would be liable in the event of any problems.