The law of effect applies to laws of which the Supreme Court has declared that they are unconstitutional.
The law has been invoked in recent years in cases involving public bodies like the Republic of Ireland’s Water Board, which sought to restrict the flow of water in the River Dee.
But it has not been invoked before this term, with the Constitutional Court ruling that the law is incompatible with the European Convention on Human Rights.
The court ruled that the constitution does not confer the right to a private right of action against a public body and that the State has no such right.
“There is a problem with the concept of the state as an employer of the public,” the Constitutional court said in a ruling published on Thursday.
The Supreme Court had previously ruled that public bodies must be allowed to regulate the flow and use of water.
But this term the court had made clear that the constitutional right of private action against public bodies was not unlimited.
It ruled that while the law of the State could be read to protect private rights of the citizen, there was “no justification for restricting the exercise of those rights in the interests of public safety”.
The ruling will have implications for all Irish public bodies, as the Constitutional courts decision on the constitutionality of the laws of effect will have a direct impact on the use of the water.
The courts said it is not possible to determine the impact of the law on public bodies’ decision-making process.
“The law of effects applies to public bodies only in respect of matters which fall within the scope of their functions, duties and functions and duties and responsibilities,” the court said.
“It does not affect the validity of legislation or the implementation of legislation, and it does not prevent the exercise or application of the rights conferred by the law in question.”
The court did not explain what would constitute a “matter” within the meaning of the Irish Constitution.