The Democratic Unionist Party (DUP) has been fined £1,000 for failing to notify the Electoral Commission that Arlene Foster had become its leader.
Mrs Foster was elected leader of the DUP in December 2015, following the retirement of Peter Robinson.
The commission imposed the fine because the DUP missed a deadline to notify it of a change in its registered leader.
The independent watchdog oversees elections and regulates political finance in the UK.
The commission confirmed the DUP had paid the £1,000 penalty.
A DUP spokesperson said: "Due to an administrative oversight the required notification was filed late.
"The Electoral Commission have indicated to us that they consider the matter closed."
Mrs Foster's appointment was ratified by the DUP's 90-member executive on 18 December 2015.
She was the only candidate for the job as no other DUP member put their name forward for the role.