Ireland's main opposition party on Friday filed a motion of no-confidence in the deputy prime minister, a move that brings the government to the verge of collapse three weeks before a crucial European Union summit on Brexit.

The Fianna Fail party is calling for the resignation of Prime Minister Leo Varadkar's deputy, Frances Fitzgerald, over her involvement in a long-running police scandal.

Opposition leaders accuse a previous government, in which Fitzgerald was justice minister, of failing to defend a whistleblower exposing corruption in Ireland's police force.

Varadkar's Fine Gael party is standing by Fitzgerald, but his minority government relies on support from Fianna Fail to govern. If it loses a confidence vote, Ireland faces a snap election.

Ireland's Parliament is due to debate the no-confidence motion on Tuesday, unless Fitzgerald resigns.

But Irish Prime Minister Leo Varadkar said later Friday he would not seek her resignation.

"What that would mean is me throwing a good woman under the bus to save myself and my own government, and that would be the wrong thing to do," Varadkar told the national broadcaster RTE.

"I think if we don't resolve matters by Tuesday, then there will be a motion of no confidence in the Tanaiste [deputy prime minister] and, if the opposition come together to remove the Tanaiste, then we will be into an election at that point," added Varadkar, who in June was sworn in.

Varadkar spoke briefly with Fianna Fail Leader Michael Martin on Friday and the pair are due to speak again on Saturday.

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Frances Fitzgerald is seen in a Dec. 2015 file photo speaking with a German official while in Brussels. The opposition believes Fitzgerald should resign for her actions in a whistleblower scandal. (Laurent Dubrule/EPA)

EU leaders will decide at a Dec. 14-15 summit whether there has been enough progress in Brexit talks to start discussions over Britain's future relations with the bloc.

Ireland says the EU will block those talks if Britain does not spell out how it can keep the Ireland-Northern Ireland border free of customs posts and other barriers after Brexit.

The 500-kilometre frontier will be the U.K.'s only land border with an EU country. Any hurdles to the movement of people or goods could have serious implications for the economies on both sides, and for Northern Ireland's peace process.

Junior finance minister Michael D'Arcy told Reuters he believed there would be an election before Christmas, and a source familiar with the party's planning said it had begun to make preparations on Friday for an election.

'Unconscionable' tactic, minister says

A snap election next month in the Irish Republic would also rule out a resumption of talks to restore a devolved government in Northern Ireland, the leader of the Democratic Unionist Party (DUP), Arlene Foster, told BBC.

The DUP has for months been in on-off talks with the Irish nationalists Sinn Fein to break a political stalemate north of the border. As Sinn Fein also fields candidates in the south, Foster said their focus would be entirely on that.

Irish Foreign Minister Simon Coveney said Fianna Fail was "behaving recklessly" at a crucial time for the country.

"Ireland does not need an election right now," Coveney said at an EU meeting in Brussels.

He said "there are some really, really serious issues for the government to manage in the national interest."

Finance Minister Paschal Donohoe was even more forceful in criticizing the opposition tactic.

"At a time when issues and decisions will need to be made that will reverberate in our country for decades to come, the prospect of either an election taking place or a government not being in place afterwards is actually unconscionable," Donohue told RTE.

The Fianna Fail move comes after Fitzgerald admitted she was made aware of an attempt to discredit a police whistleblower in a 2015 email, but failed to act. Fine Gael say she adhered to due process.

The case relates to a whistleblower who alleged widespread misconduct in the force. His treatment by the authorities led in 2014 to the resignations of the then police commissioner and justice minister.

With files from Reuters