Boris Johnson is poised to give the green light to controversial legislation on the Northern Ireland protocol this week as he flies to Belfast for crunch meetings, gambling that the move will restart stalled talks.

The prime minister warned that it was a “necessity to act” if negotiations with the EU did not resume and said new measures would be put to parliament in the coming days.

It comes as it emerged that business leaders in Northern Ireland have urged Johnson not to take any unilateral action in a private letter to Downing Street.

A source confirmed that the letter from the Northern Ireland business Brexit working group, an umbrella organisation of 14 business bodies, told the prime minister there was the prospect of a deal with the EU.

“It was being suggested that action was needed because business groups asked for it and trade was suffering because of the protocol. We asked them specifically not to launch unilateral action. We do not need the nuclear option when we believe there is still a prospect of a deal,” said the source.

They said that it was astonishing that Johnson was flying to Northern Ireland threatening unilateral action and not meeting the group, despite their pleas, adding that the government had shown scant interest in business – with one 15-minute Zoom call with Liz Truss in January and no engagement since.

The business working group – which includes the Confederation of British Industry, the NI Food and Drink Association, the Ulster Farmers Union, Manufacturing NI, Hospitality Ulster, the Institute of Directors NI, Logistics UK and the Northern Ireland Retail Consortium – is reportedly perplexed by statements from government listing issues that have already been resolved or which are close to being resolved.

Amid frayed relations between the prime minister and Truss, Johnson will emphasise the need for restrained language to his foreign secretary. However, he is still set to sign off her preferred tactic for new legislation which would override parts of the protocol to remove checks on goods crossing the Irish Sea.

Truss has prepared a bill giving the government the right to suspend elements of the Brexit deal relating to Northern Ireland, a move which the EU has warned could spark a trade war.

Measures in the bill are expected to include a new “green lane” for goods for sale only in Northern Ireland and stronger penalties for those smuggling into the EU via the Republic.

Ahead of crunch talks with parties at Stormont, Johnson said the circumstances had fundamentally changed since the deal was signed. “It was designed in the absence of a trade and cooperation agreement and when it was unclear one would be agreed. It has not been adapted to reflect the realities of the TCA.

“It was designed before a global pandemic and a European war which has created a cost of living crisis on a scale not seen for half a century.”

Johnson said in the op-ed for the Belfast Telegraph that there could not “even be a question” about the fast availability of medicines in Northern Ireland nor was it fair that the chancellor could not grant people in Northern Ireland the same tax and VAT benefits.”

He said negotiations remained at an impasse while the EU claimed it was “impossible to make the changes to the protocol text to actually solve these problems in negotiations – because there is no mandate to do so.”

One official said they expected the time frame for the new legislation to be decelerated to allow diplomatic efforts to resume. Another Whitehall official acknowledged the legislation was “several weeks away” from being formally put to MPs. Dozens of Conservative MPs have suggested they would vote against a bill in its later stages.

A Whitehall source said they acknowledged the internal briefing war of the past week, which included cabinet splits and threw the internal choreography in crisis, had been unhelpful with a decades-old peace process at stake.

“The priority tomorrow is to calm things down,” they said. The source suggested Johnson would tell Truss to handle things more delicately.

Sources close to Truss have denied her team leaked details of the planned legislation and say they have not been responsible for some of the more inflammatory rhetoric – which they claim has irritated the foreign secretary.

“The ideal solution is that we work through the problems with the protocol with the EU and through a negotiated solution and get the executive back up and running,” a government source said.

“If they are not willing to show flexibility it’s our responsibility as a government to look at other options. [Truss] does favour looking at legislation as a way of doing that. But there is a difference between giving ourselves the powers to do something and then actually doing something.”

No 10 said it was Johnson’s priority to restore the conditions for negotiations – claiming he had a “conciliatory” call with Ireland’s taoiseach last week. However, the Irish Times on Saturday reported sources describing it as “the single worst call he [Martin] has ever had with anyone”.

Johnson is expected to meet the Democratic Unionists and Sinn Féin in Belfast on Monday. The DUP blocked the election of a speaker at Stormont on Friday, meaning the assembly is unable to function after the elections where Sinn Féin became the largest party.

Sinn Féin deputy leader Michelle O’Neill who is first minister designate, said she would warn Johnson that any unilateral action to walk away from the protocol would be “reckless” and “deepen political instability”.

“Any threat of unilateral action by the British government to denounce the withdrawal agreement, or disapply the protocol would be reckless. Walking away from international obligations would also represent an appalling attack on the international rule of law,” she said.

“Only through joint agreement with the EU can solutions to problems or concerns be resolved. I will be telling Boris Johnson that unilateral action deepens political instability and economic uncertainty and must not happen.”

On Sunday the business secretary, Kwasi Kwarteng, said the UK had “the right to act in a sovereign way” and to “reopen or re-examine the protocol” but he denied the actions would constitute a breach of international law.

Johnson has previously vowed not to scrap the protocol and said he is only seeking reform that has “the broadest possible cross-community support”.

Simon Coveney, Ireland’s foreign minister, “criticised sabre-rattling and grandstanding” from ministers over the past week. Johnson has already been told that dozens of Conservative MPs would attempt to stop the bill from becoming law if it reaches the later stages – though many see it as a negotiating tactic.

Coveney said the behaviour of UK ministers was “creating a lot of tension in my country, your closest neighbour, and also potentially being on the verge of making a decision that could fundamentally undermine the functioning of the institutions of the peace process in Northern Ireland”.

He told Sophy Ridge on Sunday on Sky News that the relations between Britain and Ireland were being fundamentally damaged because of “unhelpful briefings that we’re getting from very, very senior levels within the British government this week”.

Coveney said the EU had not threatened any specific retaliation – though several European parliamentarians have said there will be consequences, including the potential suspension of the trade deal, should the UK government act unilaterally.

“There’s no way the EU can compromise if the UK is threatening unilateral action to pass domestic legislation to set aside international obligations under an international treaty that, don’t forget, the UK was the primary designer of along with the EU,” he said.