The Government is facing a potential High Court challenge over the terms of reference for inquiries into how gardaí handled four suspicious deaths.
The families of Patrick Nugent, James Clancy, Shane Tuohey, and John Kelly, who died in separate incidents between 1984 and 2008, were granted a statutory inquiry under Section 42 of the Garda Síochána Act last year.
Belfast-based news and analysis website The Detail reports that solicitors for the families have written to Minister for Justice Francis Fitzgerald warning that they may seek a judicial review unless the terms of reference are changed.
They want the terms to address what they believe is a failure to comply with obligations under the European Convention on Human Rights.
Kevin Winters of KRW Law in Belfast, who is representing the families, said: "This is completely new territory. This is the first time the Irish Government has been challenged on its obligations under Article Two of the ECHR in this way."
He said an injunction may also be sought to prevent the Department of Justice proceeding with the inquiries or publishing the inquiries' terms of reference until a judicial review is held.
Mr Winters said the judicial review will be triggered if the department fails to respond to the families' concerns by tomorrow.
A spokesperson for Ms Fitzgerald did not comment on the threat of legal action but confirmed that the minister had ruled out Article Two in the scope of the inquiries.
The spokesperson said the Tánaiste does not accept that Article Two rights have been infringed in these cases.