The British prime minister has said he is willing to override part of the Northern Ireland protocol to ensure that there is no post-Brexit trade barrier down the Irish Sea.
The DUP's Ian Paisley said his constituents had been made to feel like foreigners in their own country.
Urgent action from the European Union is needed to resolve the problems, Boris Johnson acknowledged.
The agreement on post-Brexit trade to keep the Border open has caused disruption to goods travelling from Great Britain but progress has been made in recent weeks.
Mr Johnson said: “We will do everything we need to do, whether legislatively or indeed by triggering Article 16 of the protocol, to ensure that there is no barrier down the Irish Sea.”
Article 16 is part of the post-Brexit deal which keeps Northern Ireland following the EU’s customs rules.
It is designed to allow the EU or Britain to intervene unilaterally if the protocol is causing a major problem within its borders.
The Democratic Unionists have been pressing for it to be invoked in response to strains on east to west trade which emptied some supermarket shelves temporarily following the end of the post-Brexit transition period and interfered with the transit of parcels.
Mr Paisley told the UK parliament: “Prime minister, you say that your commitment to Northern Ireland is unshakeable.
We have moved away from previous insistence of "rigorous implementation" of the NI Protocol and dismissal of issues as just "teething problems".
Now we need to find solutions that are sustainable, workable and long-lasting. pic.twitter.com/sH2kaSKD3Z
— Arlene Foster #WeWillMeetAgain (@DUPleader) February 3, 2021
“But I speak for all of my constituents today when I tell you that the protocol has betrayed us and has made us feel like foreigners in our country.
“Tea and sympathy will not cut the mustard.”
Mr Johnson spoke to Stormont First Minister Arlene Foster on Wednesday morning.
They discussed their shared concern that processes established in the protocol were ignored when Brussels threatened on Friday to override part of the deal and stop coronavirus vaccine supplies crossing the Border.
Now is a time for steady, calm and measured leadership from all political parties.
Our businesses and citizens deserve certainty and I am committed to working to provide that.
Later this evening, I will meet with the European Commission and British Government to discuss issues. pic.twitter.com/HIfyUmYjY9
— Michelle O’Neill (@moneillsf) February 3, 2021
A DUP spokesman for Ms Foster said Mr Johnson had indicated he wanted to resolve the outstanding issues by the end of next month.
“The Prime Minister indicated that he was deeply shocked ‘by the cavalier approach adopted by the EU’ last Friday and without consultation,” the party statement said.
“He recognised that such actions by the EU undermines the authority of the protocol.”
The DUP added that it was plain the protocol was being used in an “absurd” way.
Sinn Féin Deputy First Minister Michelle O’Neill said it was time for steady, calm and measured leadership from all political parties amidst unionist discontent.
“Our businesses and citizens deserve certainty and I am committed to working to provide that.”