The account, worth £7 million last year, involves creating work when COI has no time to carry out a standard pitch process.
O&M will repitch for the business against Walsh Trott Chick Smith, Publicis and WCRS. The pitch, which will be run by Peter Buchanan, COI's deputy chief executive, has been called to present government departments with a choice of agencies.
In the past year O&M has run several emergency campaigns, including informing the public about the foot-and-mouth crisis and child protection on the internet.
Last year 57 per cent of the stand-by spend was on press, 19 per cent on TV and 10 per cent on radio. COI also asked O&M to create internet, cinema and poster campaigns.
Buchanan said: "Timing is the most important issue for the stand-by agency. In the most extreme cases, work may be turned around overnight or over a weekend. O&M has succeeded in its role as the stand-by agency and we have been impressed with its ability to deliver under pressure. However, some of our clients are keen to have a choice and we may hire two agencies."
COI insisted the review was not connected to O&M's doctoring of some of its COI entries to Campaign's Press Awards earlier this year.