Police have been asked to investigate allegations that the Ulster Unionist Party failed to disclose two separate bank accounts.
They were alerted by the Electoral Commission following claims that funds worth £50,000 were not properly declared by Sir Reg Empey's party.
The UUP's current treasurer, Lord Maginnis of Drumglass, tonight pledged full co-operation with the Government watchdog.
The inquiry is believed to be focused on whether any donations during the 1990s were kept away from party auditors. One bank account was brought to the Commission's attention by a former UUP treasurer. The second emerged during follow up inquiries.
The authority has now demanded more information and evidence from party chiefs about its assets.
In a statement the regulator of electoral rules said: "The Commission has decided to refer this matter to the Police Service of Northern Ireland and has asked it to investigate whether an offence has been committed.
"The party is working with the Commission to ensure that it has the necessary systems in place to enable it complies with the financial reporting requirements of PPERA (Political Parties, Elections and Referendum Act 2000) in the future."
It is understood the PSNI received a letter on the issue today. If detectives decide to investigate the case, they will seek to examine whether funds worth £50,000 were not disclosed to the Commission when it was set up in 2001.
Lord Maginnis confirmed tonight he has been working with the Commission since he was appointed treasurer eight months ago.
"The matter of the undisclosed account has been in the public domain for some time and was brought to the attention of the Commission six months ago," he added. "We continue to work closely with the Commission on all matters of compliance."