Northern Ireland Secretary of State Theresa Villiers has been accused of attacking the Good Friday Agreement and causing a constitutional crisis.
It comes after the blocking of the circulation of documents relating to three killings during the Troubles.
The inquest documents concern the killings of IRA man Paddy McAdorey in 1971, social work student Michael Donnelly in 1980, and Sadie Larmour, who was murdered by loyalists in 1979.
The campaign group, Relatives for Justice, said there is nothing sensitive in the documents.
The group's director, Mark Thompson, said relatives are bewildered by the legal action.
Ms Villiers and PSNI Chief Constable Matt Baggott have obtained a High Court injunction blocking the minister in charge of public records from allowing families to see inquest documents relating to the killing of their loved ones.
Minister for Culture, Arts, and Leisure Carál Ní Chuilín is the legal keeper of public records.
She delivered case papers relating to the deaths of three people to a law firm and a victims' group on Friday.
The Secretary of State and the Chief Constable went to court on Saturday and obtained an injunction in order to stop the papers being circulated.
Solicitor Niall Murphy from Kevin Winters law firm said: "That an unelected Secretary of State feels she has a right to overrule a democratically-elected minister on a decision wherein the minister benefits from the advice of the Attorney General is a constitutional crisis and an attack on the Good Friday Agreement."
The High Court in Belfast this afternoon adjourned the case seeking to overturn the injunction.
The case will be heard on Thursday.
