A DUP MP has called on the prime minister to "be the unionist we need him to be" in addressing concerns over the Irish Sea border.
Ian Paisley told the Commons that the Brexit agreement had betrayed unionists and made them "feel like foreigners in our own country".
Meanwhile a "cordial" meeting between the UK government, EU and NI's first and deputy first ministers has ended.
There will be further discussions next week.
Cabinet Office Minister Michael Gove and European Commission Vice-President Maroš Šefčovič said they would "work intensively to find solutions to outstanding issues".
Speaking before that meeting took place, Mr Paisley said "tea and sympathy would not cut the mustard" and urged Downing Street to act.
Boris Johnson said the government would "do everything we need to do".
Unionists oppose the part of the Brexit deal known as the Northern Ireland Protocol, arguing it damages trade and threatens UK unity.
Northern Ireland's First Minister Arlene Foster, who leads the Democratic Unionist Party, has announced plans to stop north-south activities related to the NI Protocol until action is taken to address what she called a "growing crisis" over the Irish Sea border.
Responding to Mr Paisley in the Commons, the prime minister insisted he was committed to Northern Ireland and the union.
He said the government would act "legislatively" or by invoking an emergency mechanism known as Article 16 to override part of the protocol, if other solutions cannot be reached with the EU to remove GB-NI trade barriers.