Upper Bann MP David Simpson has been urged to clarify allegations he made about “despicable attacks” on his family during the election campaign.
Ulster Unionist leader Mike Nesbitt has written an open letter to the DUP man, asking for clarification.
Mr Simpson made the claims in the early hours of Friday morning after he secured a majority of over 2,000 over Ulster Unionist candidate Jo-Anne Dobson.
Mr Nesbitt called on Mr Simpson to provide evidence that Ulster Unionists had been involved.
He said, “Your allegations were made against members of the Ulster Unionist Party. I take those allegations most seriously.
“As I hope you are aware, I have in the past demonstrated zero tolerance to members of my Party who act in unacceptable ways, whether it be expressions of homophobia, or public displays of disloyalty.
“If any member of the Ulster Unionist Party has indeed acted in the manner you appear to allege, I assure you I shall not be found wanting in my reaction, but first I need the evidence.”
Mr Nesbitt also called on Mr Simpson to name the company responsible for an opinion poll published in the Portadown Times prior to the election. The poll showed Sinn Fein’s Catherine Seeley just behind Mr Simpson with Mrs Dobson in third place.