Sinn Féin MPs should resign if they are not willing to take up their Westminster seats to vote on Brexit, the Taoiseach says.
Leo Varadkar has lashed out at Sinn Féin for denying their constituents a voice in what will be a critical vote on Brexit next month.
UK prime minister, Theresa May, who took questions on the Brexit withdrawal deal in parliament again yesterday, is now under pressure to ensure that the draft treaty is ratified when it is put to a vote, likely to be held on December 11.
Mr Varadkar, who was speaking after returning from a special EU Council which approved the draft withdrawal agreement, said he regrets the fact the UK government has decided to leave the customs union but the deal is the best available.
The Taoiseach went on to describe Sinn Féin as "an unusual party" as they are refusing to sit in Westminster "for one reason" and are also not taking up their seats in the Stormont Assembly "for another".
"Generally people who get involved in politics get involved because they want to make a difference, SF is unusual in that for different reasons it is not participating in parliamentary democracy in Westminster or Stormont.
If they're not willing to take up their seats because they feel they can't because they got elected on the policy of abstention of not taking up their seats, then they do have the option now of resigning their seats and allowing people in those constituencies to decide whether or not they want their say when this vote goes to Westminster.
"Bear in mind there are 18 MPs in NI, eight of those are in support of what Theresa May is proposing but seven are abstaining," said Mr Varadkar.
Tánaiste and Foreign Affairs Minister Simon Coveney said the deal signed off on by EU leaders in Brussels on Sunday is "not going to change" and urged MPs in the House of Commons to support it.
"We know what the deal looks like -- if you reject it, you are essentially voting for real uncertainty and politically potential chaos, because of the consequences of not ratifying or endorsing this deal," Mr Coveney said.
He said it is not the role of the Irish Government to interfere in British politics in the lead-up to the vote on this deal, but Mr Coveney said that Fine Gael "certainly does have a role in reassuring people on this island that whether you are nationalist or unionist, this deal is about protecting relationships on the island as a whole".
"The British Government has difficult days ahead to sell this, but I think as the debate crystallises into the choice of supporting a deal we understand, that is a reasonable compromise, that provides certainty and predictability around Brexit, versus voting against that with chaos and uncertainty, I think it can be sold persuasively over the next two weeks."
Meanwhile Ulster Unionist Leader, Robin Swann called on Mrs May to put plans in place for the extension of Article 50 rather than risk the future of the Union for the sake of meeting a deadline: "A no deal Brexit is in no-one`s interests and the Withdrawal Agreement is certainly not in the long-term interests of the United Kingdom with the backstop hanging over us like a dark cloud."