The National Bureau of Investigation began examining the extent of grey economy-related crimes in the construction sector in 2015, and new information now shows that the situation is more dire than previously assessed.
Police have confiscated some 100,000 euros in cash as part of a series of home searches and apprehended one person.
Earlier pretrial investigation estimates put the number of people involved in working under the radar and without paying income tax at about 700 construction workers. Over 7 million euros in "dark" salaries were paid out in 2013-2015. The firms also dodged some 4.6 million euros' worth of taxes and pension payments.
The construction companies involved are being investigated for aggravated tax fraud and aggravated accounting offenses.
Police say the criminal enterprise is the largest tax evasion scheme Finland has seen in a decade.