Thirteen men and a woman have been arrested by British revenue and customs officers investigating a suspected £15 million money laundering racket by an organised crime gang.
Nine men and the woman were held in Belfast, with the three other men arrested in Derry, Armagh and Antrim. Another man was arrested in London.
The investigation is connected to income tax and VAT fraud linked to the construction industry.
The HMRC described the raids as the largest operation of its kind ever undertaken in Northern Ireland.
Assisted by officers from the Police Service of Northern Ireland (PSNI), HMRC staff searched 31 business and residential properties in Belfast, Co Armagh, Co Antrim and Co Derry.
In co-ordinated activity in Stoke Newington in London, one man was arrested after two businesses and one private address were raided by HMRC accompanied by officers from the Metropolitan Police.
HMRC said an organised crime gang was believed to have created a chain of companies, claiming to sub-contract labour for construction projects, with the intent of disappearing before any tax was paid.
Business records, cash and computer equipment were seized during the operation.
PA