The Dáil will vote on a motion of no confidence in the Garda Commissioner later.
But the Sinn Féin motion will be defeated as it doesn't have the support of Fianna Fáil or Fine Gael.
Both parties say the Dáil has no legal role and therefore the motion would have no effect.
But Sinn Féin deputy leader Mary Lou McDonald says that doesn't deal with the issue: "Noirin O'Sullivan remaining as Garda Commissioner presents a significant and possibly insurmountable barrier to achieveing the goals that you state for yourself of reform and change.
"So the simple fact is that we bring this because we believe it to be in the best interests of An Garda Siochana that there is change and accountablility at the very top."