Ministers will on Tuesday unveil plans for a new law to override parts of the post-Brexit deal on Northern Ireland in a bid to revive power-sharing.
After emergency talks, Boris Johnson said the legislation was needed as "insurance" in case talks with the European Union fail.
But the move would effectively tear up the Northern Ireland protocol - agreed by the Prime Minister in 2019 - which sets trading rules on goods moving from Britain to Northern Ireland.
Northern Ireland's institutions have been plunged into crisis with the DUP refusing to re-enter a devolved government in protest at the 'Irish Sea border' in the protocol.
But EU leaders have warned Mr Johnson against trying to rewrite the treaty unilaterally - suggesting it could result in a damaging trade war with the bloc.
Mr Johnson told reporters: "We would love this to be done in a consensual way with our friends and partners, ironing out the problems, stopping some of these barriers East-West.
"But to get that done, to have the insurance, we need to proceed with a legislative solution as well."
He continued: "We don't want to scrap it. But we think it can be fixed."
Ms Truss will today set out the Government's plans domestic legislation to make major changes to the deal.
However, she is not yet expected to publish any draft legislation, with some insiders suggesting she only wants to retain the option as a negotiating tool.
One said: "We want a weapon on the table, we don't want to use it. It's like the nuclear deterrent".
Any new law is likely to take up to a year to get through Parliament in the face of Tory rebellions and a bumpy path through the House of Lords.
Plans include a green lane for trusted traders to speed up customs checks and giving the Chancellor the power to cut VAT in NI in line with the rest of the UK.
Mr Johnson was booed and jeered by around 200 people, some holding banners reading "Back off Boris. Protect the Protocol", as he was driven into talks near Belfast.
Afterwards, Social Democratic and Labour Party leader Colum Eastwood warned: "If the British Government signal their intent to break international law by legislating to rip up the protocol at Westminster, he will not have the support of the vast majority of people in Northern Ireland."
Sinn Fein leader Mary Lou McDonald accused the Government of "placating the DUP" but leader Sir Jeffrey Donaldson dismissed the idea the PM was picking sides as "for the fairies".
Brussels has warned that unilateral action on the protocol would represent a clear breach of international law - and could result in a trade war with the UK.
Ireland's foreign minister Simon Coveney suggested the whole UK-EU trade deal could be jeopardised which would be a blow for the British economy during the cost of living crisis.
He told reporters in Brussels: "This is a time for calmness, it's a time for dialogue, it's a time for compromise and partnership between the EU and the UK to solve these outstanding issues.
"If that is the approach taken then we can make progress quickly to respond to the concerns of both the business community and the Unionist community in Northern Ireland.
"The alternative is unilateral action which means tension, rancour, stand-offs, legal challenges and of course calls into question the functioning of the [ Brexit deal] itself."
The UK has rejected a series of compromises by Brussels last October to cut paperwork and checks on goods entering NI, suggesting they would make the situation worse.
