The Republic's data protection commissioner Billy Hawkes has ruled that no action can be taken against Irish subsidiaries of Facebook and Apple.
The two American firms stand accused of handing the data of hundreds of millions of European citizens over to the USA's national security organisations via their US-based parent companies.
The Office of the Data Protection Commissioner (ODPC), had been challenged by an Austrian student activist group to investigate claims the US National Security Agency harvests e-mails and other data from the companies in a mass electronic surveillance programme known as Prism.
But in an e-mail published by the student group, europe-v-facebook, the ODPC said the companies were covered by Safe Harbour, which allows US firms to certify themselves as compliant with EU law by signing up to a set of principles supposed to safeguard how personal data are used.
"We do not consider that there are grounds for an investigation under the Irish Data Protection Acts given that 'Safe Harbour' requirements have been met," the ODPC wrote to europe-v-facebook.