The Government may be forced to retender lucrative public service contracts, including one granted to An Post, following a claim by a senior European Union official that the contracts could have breached EU law.
An Post, which won the contract to manage the country's social welfare payments, is in talks with Belgian-Dutch financial services group Fortis to create a joint venture in Ireland.
The European Court of Justice advocate-general Christine Stix-Hack upheld the European Commission's claim that Ireland breached competition rules by not publicly advertising the postal contract and, separately, an ambulance service contract.
The granting of a contract to provide emergency ambulance services to Dublin City Council without any prior advertising was also deemed in contravention of the European Union's treaty rules.
The opinion of the advocate-general is not binding, but the Court follows this opinion in a majority of cases.
"I propose that the Court should declare that, in deciding to entrust the provision of services to An Post without a prior notice, although there were no circumstances which would have allowed no advertising at all, Ireland has failed to comply with its obligations under the (EU) Treaty," said the opinion.
Both Fortis and An Post said they were studying the ruling and declined to comment further at this stage.