A former Sinn Féin Assembly committee chairman has resigned following allegations that he communicated with loyalist Jamie Bryson before he gave explosive evidence about the Nama property deal.
Daithi McKay led a Stormont probe into the North's largest ever property sale.
He was accused in the media of getting in touch with Co Down blogger Mr Bryson as he prepared to name former DUP leader Peter Robinson during a finance committee inquiry into the deal.
The then first minister strongly denied that he had sought to benefit in any way from the agreement involving US investors and Nama.
Sinn Féin Stormont chief whip Caral Ni Chuilin said: "Daithi McKay has resigned as MLA for North Antrim with immediate effect and has been suspended from Sinn Féin."
The Irish News reported what it said were leaked messages between Mr Bryson and Sinn Féin Twitter users including Mr McKay. Sinn Féin leader Martin McGuinness has denied any knowledge of the matter.
The deal two years ago by Nama with US investment giant Cerberus involving the €1.38bn sale of a Northern Ireland property loan portfolio has been dogged by controversy after €8m linked to it was found in an Isle of Man bank account.
Critics have claimed the arrangement included multimillion-euro fixer fees.
None of the Twitter messages indicated that Nama-related information came to Mr Bryson from Sinn Féin and the party has said its aim was to get to the truth of the €1.38bn sale of Northern Ireland properties by Nama. Mr Bryson, for his part, has dismissed claims that he was advised as absurd.
The Irish News reported that Mr McKay was in contact with Mr Bryson via social media in the weeks before the high-profile hearing last year and that he then referred him on to another Sinn Féin member.
DUP peer Lord Maurice Morrow said: "As chairman of the Democratic Unionist Party (DUP) I will also be referring the matter to the Police Service of Northern Ireland (PSNI) for investigation."
On Thursday, in response to the revelations, Mr Bryson tweeted: "The evidence provided to the Department of Finance and Personnel (DFP) committee was not, in any shape or form, influenced or sourced from any member of Sinn Féin."
The evidence provided to the DFP committee was not, in any shape or form, influenced or sourced from any member of SF.— Jamie Bryson (@JamieBrysonCPNI) August 18, 2016
He added it was: "Absurd to suggest I was coached by Sinn Féin. If, as is alleged, Sinn Féin were manipulated into assisting my passage to DFP that's a matter for them."
Absurd to suggest I was 'coached' by SF. If, as is alleged, SF were manipulated into assisting my passage to DFP; that's a matter for them.— Jamie Bryson (@JamieBrysonCPNI) August 17, 2016
Nama was established in Ireland at the height of the financial crisis to take property-linked loans off the books of bailed-out banks.
It sold 800 property loans to Cerberus, a multi-billion fund which boasts former US vice president Dan Quayle in its ranks.
The €8m was paid into an account controlled by a former managing partner of Belfast-based law firm Tughans, Ian Coulter, who resigned after it was unearthed.
Tughans, which was involved in the Nama transaction as subcontractor for Cerberus's US lawyers, Brown Rudnick, insisted it was not aware of the transfer.
All parties involved in the €1.38bn transaction in 2014 have denied wrongdoing.
Mr McKay has not responded so far, but Sinn Féin said its position has always been about getting to the truth about the sale of the Nama portfolio.
Deputy First Minister Martin McGuinness said neither he nor the party had any knowledge of alleged contact with Nama witnesses.
"The allegations surrounding North Antrim MLA Daithi McKay are profoundly disturbing.
"If the allegations of inappropriate contact prove to be true, then Daithi McKay needs to seriously consider his position as an MLA."
Ulster Unionist leader Mike Nesbitt demanded an inquiry.