In her ruling on costs on Friday, Ms Justice Caroline Costello said she was “acutely aware that the effect of this decision is to place a very heavy financial burden” on the Data Protection Commission (DPC).

The case concluded when the Court of Justice of the European Union (CJEU) ruled in July that there are insufficient safeguards on EU citizens’ personal data in the US because the US gives primacy to national security and law enforcement without respect to the principle of proportionality.

The costs of the case could reach up to €2 million, according to some media reports, which is more than a tenth of the DPC’s annual budget.

Ms Justice Costello said: “Despite the fact that she acted entirely correctly, her office must bear the majority of the costs of the application.

“It is, in my view, an unavoidable incident of her role and this outcome ought not to impact on the future functioning of the Commission for Data Protection. I sincerely hope that it will not have a chilling effect upon the future conduct of her successor, the Data Protection Commission.

“It is a matter for government to ensure that the Commission is adequately resourced so that considerations of legal costs do not act as a deterrent which hinder or prevent the Commission from carrying out its vital functions as a truly independent, national supervisory authority and guardian of fundamental rights.”