Party worker Thomas O’Hara has been accused of communicating with loyalist blogger Jamie Bryson before he gave explosive evidence to Stormont’s finance committee about the efforts of Ireland’s bank for bad loans to dispose of its Northern Ireland portfolio to US investors.
Committee chairman Daithi McKay also faces claims of wrongdoing. The Sinn Fein North Antrim Assembly member has apologised and resigned from the Assembly. He said his contact was inappropriate but denied coaching Mr Bryson.
A Sinn Fein spokeswoman confirmed Mr O’Hara had been suspended.
The party has said it would welcome an investigation into claims about its members’ conduct.
Mr Bryson was preparing to name former Democratic Unionist leader Peter Robinson in connection with the case.
The then first minister strongly denied seeking to benefit from the agreement involving US investors and the National Asset Management Agency (Nama).
Mr McKay was the mercurial face of Sinn Fein’s youth generation who spent more than a decade working for the party in North Antrim on causes like the environment.
His fall from grace was precipitated by claims in Belfast newspaper the Irish News about his contact with Mr Bryson.
The Irish News reported what it said were leaked messages between Mr Bryson and Sinn Fein Twitter users including Mr McKay. Sinn Fein leader Martin McGuinness has denied any knowledge of the matter.
The deal two years ago by Nama with US investment giant Cerberus, involving the £1.2 billion sale of a Northern Ireland property loan portfolio, has been dogged by controversy after £7 million linked to it was found in an Isle of Man bank account.
Critics have claimed the arrangement included multimillion-pound fixer fees.
None of the Twitter messages indicated that Nama-related information came to Mr Bryson from Sinn Fein.
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 multibillion-pound fund.
The £7 million 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 2014 transaction have denied wrongdoing.