The communications regulator ComReg has ruled that O2 and Vodafone must open up their networks to competition from January next year.
A study conducted by ComReg found that the mobile operators Vodafone and O2 have joint dominance in the Irish market.
The body is notifying the EU Commission of its findings and, subject to the Commission's approval, ComReg will implement the proposed measures from January.
This means that Vodafone and O 2 networks would then be available to other mobile operators to offer services to the public.
ComReg says that similar measures have resulted in a fall in prices of up to 25 per cent in other European countries.
Following the introduction of new EU communications legislation in 2003, ComReg was required by the European Commission to determine whether the Irish market was effectively competitive and, if not, to introduce measures to stimulate more competition.
The authority has now proposed to open the networks of these operators to alternative service providers.
Labour Party spokesperson on communications, Mr Tommy Broughan, welcomed the move saying it would be good for competition and ultimately good for the Irish mobile phone user.
"The decision to open these networks to Mobile Virtual Network Operators (MVNOs) will go some way to address the manner in which the mobile phone market in Ireland currently operates. Up to now, the granting of a mobile phone licence has been an opportunity to generate enormous profits, particularly for Vodafone and O2."
