The taoiseach (Irish PM) has said he is not optimistic of a Brexit deal in light of the UK proposal to override parts of the Withdrawal Agreement.
Micheál Martin told Irish broadcaster RTÉ "trust has been eroded" by the move by Prime Minister Boris Johnson.
"The stakes are higher now because of the British action," he said.
The bill proposes no new checks on goods moving from Northern Ireland to Great Britain.
It gives UK ministers powers to modify or "disapply" rules relating to the movement of goods that will come into force from 1 January, if the UK and EU are unable to strike a trade deal.
Taoiseach Micheál Martin said the bill is likely to impact further negotiations.
"The publication of the bill signals an attempt by the UK government to essentially break its commitment entered into an international agreement and that is very serious," he said.
"I think the European Union leadership will be very concerned in how negotiations go from here."
Mr Martin said he stressed his "outright opposition" to the move taken in a phone call with Mr Johnson on Wednesday night.
He said he pointed out very strongly it was "dragging Northern Ireland" back into the centre stage.
He said Britain signed up to the EU-UK Withdrawal Agreement and the Northern Ireland Protocol with a view to ensuring they wanted access to the European market.
"Trust has been eroded but he made it clear to me that the UK was fully committed to meeting the obligations of protecting the single market and fluidity of trade north and south. The legislation runs counter to that."
'Don't imperil Good Friday Agreement'
His comments came after US Speaker of the House Nancy Pelosi warned there will be "absolutely no chance" of a US-UK trade agreement if Brexit undermines the Good Friday Agreement.
Speaker Pelosi issued a statement on Wednesday praising the Good Friday Agreement as NI's "bedrock of peace".
She said Brexit cannot be "allowed to imperil" the agreement.
"The UK must respect the Northern Ireland Protocol as signed with the EU to ensure the free flow of goods across the border," Ms Pelosi said.
"If the UK violates that international treaty and Brexit undermines the Good Friday accord, there will be absolutely no chance of a US-UK trade agreement passing the Congress," she added.
'Threat to Agreement'
Democratic Congressman Richard Neal told RTÉ he had raised concerns over the latest Brexit developments, and their implications for Northern Ireland, with Ms Pelosi.
Congressman Neal is the chairman of the House Ways and Means Committee, which will oversee any future US-UK trade agreement.
"I spoke to Speaker Pelosi earlier this morning about what I saw as a threat that could jeopardise the success of the Good Friday Agreement," he said.
"She indicated that she is consistent with my view that any threat that would reimpose a border on the island of Ireland would negate any possibility of having a free trade bilateral agreement with the United Kingdom," he added.
'No return of border'
A foreign policy adviser to Joe Biden has said that the Democratic presidential candidate is also committed to preserving peace and stability in Northern Ireland.
In a tweet responding to the latest Brexit developments, Mr Biden's adviser Antony Blinken wrote: "As the UK and EU work out their relationship, any arrangements must protect the Good Friday Agreement and prevent the return of a hard border."
@joebiden is committed to preserving the hard-earned peace & stability in Northern Ireland. As the UK and EU work out their relationship, any arrangements must protect the Good Friday Agreement and prevent the return of a hard border. via @NYTimes https://t.co/KUIScLLqt0— Antony Blinken (@ABlinken) September 8, 2020
"I sincerely hope the British government upholds the rule of law and delivers on the commitments it made during Brexit negotiations, particularly in regard to the Irish border protocols," he added.
This is not the first time that Mr Biden and other senior Democrats have voiced support for the Northern Ireland peace process.
Last month, the Biden campaign held a virtual rally for Irish-American voters and Democratic Congressman Brendan Boyle told the event that the Brexit process had put hard-won peace and justice in Ireland at risk.
"We fortunately have many allies on Capitol Hill. One place that has not been an ally is the Oval Office," Congressman Boyle said.
"What a refreshing change it will be to have Joe Biden come this January. To have someone who supports the Good Friday Agreement and wants to protect it. Someone who is not mindlessly cheerleading for Brexit no matter the cost," he added.
Last November, while campaigning for the Democratic nomination, Mr Biden said he cared a great deal about the Northern Ireland peace process and that he would continue to put pressure on Britain to ensure there is no return to a hard border after Brexit.