The Competition Authority is to investigate a €200 million deal that saw Denis O'Brien buy three more Irish radio stations.
Mr O'Brien's Communicorp Group Limited said it had bought national station Today FM, Dublin-based FM 104 and Donegal's Highland Radio from Emap .
But Communicorp Group already owns Dublin's 98 FM and Spin FM and national broadcaster Newstalk.
The deal now has to get approval from the Broadcasting Commission of Ireland, the Minister for Enterprise, Trade and Employment and the Competition Authority.
Lucy Gaffney, chairman of Communicorp, said it was a very significant development for Irish commercial radio.
"Communicorp has for many years demonstrated its commitment to investing in independent commercial radio in Ireland, and to the goal of quality broadcasting to all segments of the market," she said.
It is understood Communicorp beat bids from The Irish Times, TV3, UTV and Scottish media group New Wave to secure the deal.