Politicians have echoed business groups' concerns about potential regulatory divergence between Britain and the EU.
A House of Lords committee's report published on Tuesday said businesses were worried that different regulatory regimes would jeopardise supply chains and leave manufacturers and food producers in "no man's land".
The peers' Sub-Committee on the Protocol on Ireland/Northern Ireland's report on the Windsor Framework concluded that the EU-UK deal struck in February is an improvement on the protocol but that problems remain.
It is unclear whether still DUP advocates dual regulation – and potential regulatory divergence – in its 18-page document submitted to the British government last month, however, the party has previously supported it.
In March, the Financial Times reported that DUP Westminster Whip Sammy Wilson wrote privately to the the British government warning that dual regulation for the north "does raise some concerns for us" even though his party had previously supported it. The East Antrim MP later said he was writing on behalf of the Ulster Farmers Union, which he said would opt for EU regulations "to keep their purchasers happy".
The farming lobby group and other agrifood representative bodies oppose dual regulation.
Mr Wilson said on Tuesday that the DUP, which is boycotting the Stormont institutions over its concerns around the post-Brexit trade arrangements, would "continue to fight the government on this issue".
"We are not prepared to have our economy destroyed and our place within the United Kingdom affected by a deal with Europe, which leaves us exposed to being inside the EU single market with no democratic control and with barriers placed to between us and the country to which we belong," he said.
"That is why our principled stance is the right stance and rather, as other parties have called for implementation of the protocol, we want the abolition of it."
Alliance deputy leader Stephen Farry said the Windsor Framework was "the best attempt to square an otherwise impossible circle".
He said regulatory divergence between Britain and the north "remains a major concern for business".
"There is a clear trade-off in the closer the UK is aligned to the EU then the less the friction across the Irish Sea and the less the prospects of divergence," he said.
"A dual regulation system inside Northern Ireland is not practical and had been ruled out."
SDLP MLA Matthew O'Toole said dual regulation was an "unwanted and unworkable distraction".
"The DUP's boycott of government has always been morally wrong but is increasingly politically absurd," he said.
"No further changes to the protocol/Windsor Framework are coming as a result of their abstention and the only people being punished are the people of NI."
Ulster Unionist leader Doug Beattie said the peers' report confirmed that "boycotting of the devolved institutions has had no effect on the Northern Ireland Protocol or on the negotiations".
He said the Windsor Framework would be implemented "whether Stormont is up and running or not".
"If, as they have intimated, His Majesty’s Government is not going to reopen negotiations on the Windsor Framework, what is the plan B?" the Upper Bann MLA said.
"If it’s direct rule Ministers, as some are eagerly wishing for, be in no doubt Dublin will have a greater say in what happens in this part of the United Kingdom.
"It’s incumbent on all unionists to return to the executive as soon as possible to provide good government for the people of Northern Ireland and challenge the Windsor Framework from within."
