By Aoife Moore, PA
Sinn Fein has criticised Leo Varadkar for "conceding at the 11th hour" that there would be border checks in a no-deal Brexit.
The Irish premier outlined the impacts of the United Kingdom leaving the European Union without a deal during a speech to business leaders in Dublin on Thursday evening.
He said there will be checks on goods and live animals, which he said would take place "as far as possible" in ports, airports and at businesses.
"But some may need to take place near the border," he said.
Sinn Fein leader Mary Lou McDonald came down on Mr Varadkar for "thinking out loud" about possible checks, that she says would be in contravention to the Good Friday Agreement.
"We were very concerned to hear the Taoiseach think out loud and concede the point that there might be checks anywhere on the island of Ireland," she told media on Saturday.
"We all committed to a bottom line, to protect our economy and peace process and never conceding any damage to the Good Friday Agreement, and the Taoiseach shouldn't concede that now at the 11th hour.
"It's very important that he remains steady and retain focus and we present a united front when dealing with EU authorities and in particular with the British system and Boris Johnson.
"There cannot be any check anywhere on the island of Ireland, it would be an act of absolute political vandalism and anywhere checks might be located, it would represent a serious breach of the Good Friday Agreement."
Mr Varadkar says there will be a 'grace period' for no-deal Brexit changes to cross-border trade, however Ms McDonald says the issue is not related to the timing, but the checks themselves.
"You can dress it up any way you want, whether it's a big bang or gradual process, the introduction of checks and customs and tariffs at any speed means you have not only breached the all-island economy but a fundamental building block of the Good Friday Agreement so that can't happen."
"The EU agreed with us all of us, there was an agreement that the bottom line was no disruption to trade and protection of people's livelihoods, but above and beyond all else, protection of the status quo that underpins the Good Friday Agreement, we take no comfort that this will happen slowly, it can't happen at all.
"It shouldn't be down to a choice between protecting the single market and the Good Friday Agreement, it should be both.
"If the Tories cannot reconcile that, then we're straight into the terrain of removing the border.
"One way or another we cannot go backwards, we cannot envisage a repartitioned Ireland almost a century on."
Likewise, Fianna Fail leader Micheal Martin said the Irish government must be "absolutely honest" and "up front" about their plans for customs checks.
The political rivals have been calling on the Irish government for months to publish their no-deal Brexit preparations.
Meanwhile, the House of Lords passed a bill on Friday effectively blocking a no-deal Brexit, paving the way for it to become law.
On the same day, the Prime Minister told reporters he would not entertain seeking another deadline extension from Brussels, as the incoming law, expected to receive Royal Assent on Monday, compels him to if no agreement is in place by October 19