Culture Secretary Jeremy Hunt has asked Ofcom and the Office of Fair Trading to investigate the sale of Guardian Media Group's radio business to Global Radio.
The deal, which includes the Readl Radio and Smooth Radio station and is estimated at around £70m, was first announced by GMG in June.
But the Department of Culture, Media and Sport announced this morning that Hunt had asked Ofcom to investigate the public interest consideration of media plurality arising from the potential merger.
The OFT has been asked to advise Hunt on competition and jurisdictional aspects of the transaction.
Both are expected to report back on 28 September.
Hunt said: 'On the basis of the information available to me, I have decided that under all the circumstances and, in particular the concentration of ownership which will occur in some parts of the UK, the merger may be relevant to the issue of plurality, particularly in those areas.
'Accordingly, I consider it appropriate to issue an intervention notice in this case, and I am therefore asking Ofcom to prepare a report advising me in greater detail about plurality.
'In addition, the legislation requires that OFT produces a report on the competition and jurisdictional aspects of the transaction, notwithstanding that the merged parties have indicated they would like a fast-track reference to the Competition Commission.
'When I receive the Ofcom report I will consider their independent advice carefully before deciding whether the matter should also be referred to the Competition Commission for a more detailed investigation of the plurality concerns."
In response to the news Global Radio issued the following statement: "Global note, with interest, that the Secretary of State has asked Ofcom and the OFT for submissions on a public interest intervention following the recent acquisition of GMG Radio. We have already submitted a detailed paper articulating our views and opinions on this subject to the relevant authorities."
A further announcement will be made once Hunt has considered OFT and Ofcom's reports.
GMG Radio was launched in 1999 and claims a total share of the radio listening market of 4.5 per cent, making it the UK's third-biggest radio group.