The High Court has granted an application by the US government to be joined to a major legal action in Ireland, about whether or not existing EU-US data transfer channels unlawfully breach EU citizens' privacy rights.

Mr Justice Brian McGovern granted the unprecedented application, ruling that the US government had a "significant and bona fide interest" in the outcome of the case.

The US government and several other parties had applied to be joined as "amicii curiae" - meaning assistants to the court on legal issues, to the action by the Data Protection Commissioner.

The Commissioner's action seeks to decide the validity of channels known as Standard Contractual Clauses, being used for daily EU-US data transfers.

The Commissioner wants the High Court to refer the validity of the channels to the Court of Justice of the EU for determination.

A party would not be able to participate in any reference to the EU court without being joined by the Irish High Court.

Mr Justice McGovern said what was at issue in the case, was the assessment as a matter of EU law, of the US law governing the transfer of EU citizens' data to the US.

He said the imposition of restrictions on the transfer of such data could have potentially considerable adverse effects on EU-US commerce and could affect US companies, significantly.

He said he was satisfied the US could bring added value to the case.

The judge also joined US-based data privacy watchdog EPIC (Electronic Privacy Information Center). He said it could offer a counter-balancing perspective from that of the US government.

He also joined Business Software Alliance, a global trade association whose application was supported by the American Chamber of Commerce Ireland.

Its members include Apple and Intel and the judge said it could provide relevant views not otherwise available to the court.

The judge joined Digital Europe, saying it was the principal representative body on matters of EU policy for members of the digital technology industry in Europe.

He said many of its members had an interest in and would be affected by the decision made in the case and he was satisfied it could assist the court.

He refused to join the Irish Business and Employers Confederation, finding it could not add anything to assist the court.

He also refused to join the Irish Human Rights and Equality Commission.

He said the Data Protection Commissioner had a particular statutory remit in relation to data protection issues.

He said he was not satisfied the IHREC could offer assistance that could not be offered by the Commissioner.

He also refused to join the American Civil Liberties Union/Irish Council for Civil Liberties; another US-based data privacy watchdog, the Electronic Frontier Foundation; or UK-based data privacy campaigner Kevin Cahill on grounds including his view they would not offer any particular assistance or a different perspective not already available.