The move could risk the collapse of talks with the EU over a free trade deal.
The UK Labour Party says it would be an act of '"immense bad faith".
Meanwhile, Mr Johnson says Britain will walk away from negotiations in 38 days time.
As part of the terms of the Northern Ireland Protocol, the region is expected to continue to follow some EU rules after the transition period ends in 2021 to ensure there is no hard border.
As the Brexit negotiations between the EU and British Government enter their eighth round this week in London, any threats of a roll back on the Irish protocol would represent a treacherous betrayal which would inflict irreversible harm on the all-Ireland economy, and GFA. 1/2
— Michelle O’Neill (@moneillsf) September 6, 2020
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Northern Ireland Deputy First Minister Michelle O’Neill tweeted that any threat of backtracking on the protocol would be a “treacherous betrayal which would inflict irreversible harm on the all-Ireland economy and the Good Friday Agreement”.
Ms O’Neill stressed the need for the protocol to be fully implemented as soon as possible and to “avoid any border in Ireland”.
Scottish First Minister Nicola Sturgeon said the move would constitute a repudiation by the Government of a treaty “freely negotiated by it” and which was described as “oven ready” by Mr Johnson.
She tweeted this would “significantly increase” the likelihood of a no-deal Brexit, and the “resulting damage to the economy will be entirely Tory inflicted. What charlatans”.
If true, this means repudiation by UK govt of a Treaty freely negotiated by it, & described by PM in GE as an ‘oven ready’ deal. This will significantly increase likelihood of no deal, and the resulting damage to the economy will be entirely Tory inflicted. What charlatans. https://t.co/p0Ur3YwEnK
— Nicola Sturgeon (@NicolaSturgeon) September 6, 2020
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SDLP leader Colum Eastwood said the British government would be undermining the Good Friday Agreement, risking the future of the UK and destroying its own credibility on the world stage if it proceeded with one of the most “reckless” acts concerning Ireland by a British government “in a long long time”.
“It’s absolutely astonishing that any government who says they want to go and do trade deals around the world would just rip up an agreement that they made a few months ago with the European Union,” Mr Eastwood told BBC Radio 4’s Westminster Hour.
“And what they would be doing in that would be undermining the Good Friday Agreement which is an agreement voted for by the vast majority of people on the island of Ireland, they’d be risking a hard border in our country and they’d be threatening the peace and security that we’ve built up over decades.
“It would be the most reckless act that a British government, and they’ve made many reckless acts in Ireland … in a long, long time and if they do this their international credibility I think would be shot to pieces.”
Mr Eastwood said he hoped the reported manoeuvrings by the British government were “just posturing, because if they try to do this at the same time as trying to convince people in Scotland and Northern Ireland about the future of their Union, well they may as well forget about that as well, because people here will see this as a tremendous act of bad faith”.
Minister for Foreign Affairs Simon Coveney said the reported development would be “a very unwise way to proceed”.
This would be a very unwise way to proceed. #Brexit .
https://t.co/D4aod2665h— Simon Coveney (@simoncoveney) September 6, 2020
Despite the accusations, UK environment secretary George Eustice said the story did not reflect what was actually happening.
"The news this morning can obviously exaggerate certain things. The point is the Northern Ireland protocol is agreed.
"We are working in good faith but it was always recognised that there are a few minor technical issues that still needed to be resolved through a joint-committee process and that work is ongoing."
