The Social Democrats say it will support a no-confidence motion in Tánaiste Leo Varadkar in the Dáil next week.
It comes as Labour are also set to support the Sinn Féin motion when it goes before the Dáil on Tuesday.
Sinn Féin said on Friday that the party will table a motion of no confidence in the Tánaiste.
It comes after a week of controversy surrounded Mr Varadkar over his passing of the IMO pay deal to the rival NAGP, then headed by his friend, Dr Maitiú Ó Tuathail.
Last night, Labour TD Aodhán Ó Ríordáin said: “We will support the motion of no confidence in the Tánaiste but we believe there are bigger issues facing our country at the moment and priorities for discussion in Dáil Éireann next week”.
Speaking to Newstalk today, Soc Dems co-leader Catherine Murphy says the party will be supporting the no-confidence motion.
“We have to formally meet on Monday which we will do and it’s at that point that we’ll formally make the decision,” she said.
“The reality of it is that there was the leaking of a confidential document with confidential written on every single solitary page.
“That is not only not the standard to be set by a government, it is not a lawful way to proceed.
“We have the greatest of concerns in relation to this.”
Last week, Róisín Shortall said the issue had been "damaging to government" and, by extension, damaging to politics.
In a statement confirming the motion of no confidence in the Tánaiste, Sinn Féin’s Mary Lou McDonald said: “The Taoiseach Micheál Martin has decided to sit on his hands and take no action.
“The Opposition cannot sit idly by, so we have acted - this is the right thing to do and it is the necessary thing to do.
“Sinn Féin is tabling a motion of no-confidence in the Tánaiste and Fine Gael leader Leo Varadkar, which will be debated during our private members' time in the Dáil next Tuesday.“ Ms McDonald said they didn’t take the decision lightly.
“This government has only been in office for just four months and over that time we had the basis of taking many motions of no-confidence due to gross incompetence and bad decision making.
“We choose not to do so because of the challenges facing the country.
“But this is different. This is more of the old Fine Gael behaviour where it is about who you know and insiders getting access to the corridors of power.”