The latest opinion poll shows support for the Government parties has dropped to its lowest level since the Coalition took office in March 2011.
The Red C poll for The Sunday Business Post shows Fine Gael support at 26%, which is down three points.
The poll was carried out earlier this week at the height of the controversy surrounding Minister for Justice Alan Shatter.
It also shows a two-point fall in support for Labour, which is now at 9%.
Sinn Féin is the big winner, as the party is up five points to 21%.
Both Fianna Fáil (22%) and Independents and Others (22%) remain unchanged.
The poll shows that the resignation of Martin Callinan as garda commissioner and the revelations of secret phone recordings at garda stations are affecting Government support.
The poll comes less than two months before the Local and European Elections.