
ITV only announced the sale of Friends Reunited to Brightsolid, a subsidiary of Beano and Dandy publisher DC Thomson, in August for £25m - taking a hit of £145m.
Friends Reunited was bought by ITV four years ago for £170m as part of the broadcaster's push into social networking. But it was soon overtaken by sites such as Facebook, which did not charge members for a subscription.
The OFT today referred the anticipated acquisition to the Competition Commission "for further investigation".
The OFT said Brightsolid, which runs websites Find My Past.com and 1911 Census.com, and Friends Reunited which owns Genes Reunited.com, are "two of the three largest suppliers of online genealogy services in the UK".
The OFT added that it does not believe that current competition "in this market or the potential for future entry is sufficiently strong to prevent the merged firm from reducing the quality or range of its services, or possibly raising prices."
Amelia Fletcher, OFT Senior Director of Mergers, said: "The proposed acquisition would see the three main providers of online genealogy services reduced to two, and we are concerned this could lead to a reduction in choice or service for consumers. We are therefore referring the merger to the Competition Commission for a fuller inquiry."
The Competition Commission is expected to report by 16 April 2010.
ITV said is "disappointed" by this outcome, but will "work closely" with the Competition Commission and Brightsolid to seek to "resolve this process satisfactorily".