PRESSURE has increased on Brexit-supporting Secretary of State Theresa Villiers with four of the five main Northern Ireland parties now backing UK remaining within the European Union.
The UUP became the last party to state its position on the June referendum on EU membership - indicating it believes Northern Ireland "is better remaining in".
Even before Saturday's decision by the Ulster Unionists, there had been calls for Ms Villiers to either resign or take a leave of absence from her role until after the election.
Sinn Féin deputy first minister Martin McGuinness said she should resign because the implications of UK withdrawal would be "absolutely enormous" for Northern Ireland.
"Anybody that has examined our relationship in the North with the EU over the course of many years, can't fail to recognize enormous benefits there have been for the community and voluntary sector, farmers and business community," he said.
SDLP leader Colum Eastwood insisted she could not act in the interests of Northern Ireland if she was campaigning to leave the EU, given Britain's departure "is not in the interest of our economy or in the interest of our society".
Meanwhile, Alliance chief whip Stewart Dickson has warned that if the vote is to remain in the union, British prime minister David Cameron will sack from his cabinet those members - including Ms Villiers - who campaigned against it.
On Sunday night, the UUP had not yet stated a view on the Secretary of State's position.
However, even the Liberal Democrats have called for her resignation, with MEP Catherine Bearder saying Brexit would have a "disastrous impact on the Northern Ireland peace process (and) it would be highly inappropriate for Theresa Villiers to remain in her post while campaigning to leave the EU".
Ms Villiers spokeswoman has described calls for her to resign as "ludicrous" and "ridiculous".