The backstop would make Northern Ireland a protectorate of an unaccountable EU, the Ulster Unionist leader has said.
Robin Swann said unionists who voted remain did not do so because they wanted to leave the UK and it was dishonest to portray them as such.
An overall majority in Northern Ireland voted remain in the Brexit referendum.
Mr Swann told his party’s annual conference in Armagh: “This is not just about the immediate constitutional problems it raises, but also the long-term implications as the UK would begin to diverge from EU regulations.
“It would effectively make Northern Ireland an EU protectorate.
“If this scenario were to become a reality, we would be complying with regulations set by a body we were no longer part of and we had no input into.
“So where is the accountability?”
The backstop is in place in case no deal is reached between the EU and UK and has been interpreted by Europe to mean Northern Ireland continuing following the bloc’s trading rules to prevent a hard border.
The British Government and unionists in Northern Ireland have opposed any solution which would effectively see a regulatory border created down the Irish Sea between Northern Ireland and Great Britain.
One of the EU’s red lines entails opposition to the UK as a whole enjoying special trading status while not having to follow other rules of the bloc, “cherry-picking”, as some have put it.
Some British Brexiteers are also opposed to the Northern Ireland backstop.
Mr Swann said: “Those unionists who voted remain did not do so because they wanted to leave the United Kingdom and it is dishonest and deceitful to portray them as such.
“And they certainly didn’t vote for the backstop either.
“While you continue to swing wildly between assuring people the backstop is an insurance policy no one wants to then have to refer to it as the best of both worlds, it leaves the impression there are those out there who have their fingers crossed behind their back that the UK Government won’t get a good deal and we will default to the backstop.
“This position is as reckless as those chasing a hard, or even a no-deal Brexit.”
The Government has said it is not challenging the constitutional position of Northern Ireland as part of the UK but wants to preserve frictionless cross-border trade and peace on the island.
Mr Swann added: “Let me also be clear that we want a good relationship with our neighbours in the Republic of Ireland, but it’s very hard to maintain that when you continually poke us in the eye. Work with us, not against us.
“So I have a message for Leo Varadkar, Simon Coveney and their colleagues in the Irish Government. Tread carefully.
“Every day that you trample over the Belfast Agreement and the principle of consent, you do further damage to relationships across these islands.
"It’s grim that the DUP have created a situation where Sinn Fein of all people are able to call for “integrity in government” and gifted them the opportunity to pull down the institutions" #UUP18 pic.twitter.com/L75cQNsGTm— Ulster Unionist (@uuponline) October 20, 2018
“Breaking the Belfast Agreement to facilitate the backstop risks destroying what has taken decades to build.
“Stop trying to exploit Brexit to weaken the integrity of the United Kingdom.
“It would also be economic vandalism to impose a border on our most important trading route which is between Northern Ireland and Great Britain.”
- Press Association