The DUP has been fined £1,000 by the Electoral Commission for “inaccurate” loan reporting.
The watchdog imposed two fines of £500 each, which were paid earlier this month, its latest report disclosed.
The Democratic Unionists are Northern Ireland’s largest party and their MPs support Theresa May’s minority Government on key votes like Brexit.
The Commission said: “The Commission considered, in accordance with the enforcement policy, that sanctions were appropriate in this case.”
Ann Watt, head of the Electoral Commission in Northern Ireland, added: “The reporting requirements are clear, so it is always disappointing when parties fail to comply.
“It’s vital that voters are given an opportunity to see accurate and full reportable data on what parties spend money on in order to influence them at elections and referendums.
“This provides transparency in the political finance system and is open for anyone to scrutinise.
“The Commission will continue to enforce these requirements on all parties and campaigners to ensure voters have the information they need.”
Meanwhile, Jim Allister’s Traditional Unionist Voice party was fined £1,000 for late delivery of a spending return for last year’s general election.
The fine was due to be paid earlier this month.