Fianna Fail is to force the issue of gay marriage on to the political agenda by tabling a private members motion in the Seanad calling for legalisation.
Seanad leader Darragh O'Brien told the Sunday Independent: "We intend to move forward on the issue and force the Government to move its timetable forward."
He added: "Fianna Fail sees equality and diversity as being a foundation stone of modern-day republicanism. Eamon Gilmore has said this is a political priority that hasn't been delivered. We intend to progress this matter swiftly."
The motion could prove to be politically difficult for Labour in the wake of the declaration by Mr Gilmore last year that that gay civil marriage is the civil rights issue of this generation.
In contrast, in a stance that may accentuate tensions with Labour, Taoiseach Enda Kenny is believed to be more equivocal on the issue.
The matter is further complicated by the Government's minority position in the Seanad, which means it could struggle to defeat the motion. Fianna Fail is likely to have its own troubles should a whip be imposed on conservative senators such as Jim Walsh.
It is believed, however, that Fianna Fail leader Michael Martin might not be too upset were some of his more conservative senators to lose the Fianna Fail whip on this issue.