By Q Radio News
The Ulster Unionist Party has been fined for failing to declare £12,000 of its spend on last year's Assembly election.
The party was handed the £3,000 penalty by the Electoral Commission for lodging an inaccurate return.
Bob Posner, from the Electoral Commission, said: "Experienced political parties such as the UUP are expected to be able to follow the rules regarding spending at elections."
The UUP, which has paid the fine, has commissioned auditors to review the party's accounting processes and to recommend improvements.
"The Electoral Commission is pleased that the UUP is reviewing its procedures and hopes that this will ensure that a mistake of this nature is not repeated," said Mr Posner.
"It is important that the spending of political parties and campaigners at elections and referendums is fully transparent and the rules are correctly followed."
A UUP spokeswoman said: "The Ulster Unionist Party has fully co-operated with the Electoral Commission at all stages of its investigation into 2016 Assembly election spending and treated it with the utmost seriousness.
"We deeply regret that these incidents occurred in the first place and undertook a major internal audit resulting in comprehensive specific actions to prevent a recurrence in future. We will review our processes on an ongoing basis.
"We fully accept the Electoral Commission's findings and have paid the resulting fine in full."