Both Finland's blue collar union federation, the SAK, and the Finnish Service Union United (PAM) say there’s been a spike in the mistreatment of foreign workers over the past two years. Most complaints concern overtime and underpayment.

“Workers may be paid half of what the collective agreement calls for,” said Raimo Pohjola of the Finnish Construction Trade Union in Ostrobothnia. “Employees have even been housed in the middle of a construction waste dump.”

Bulgarians, Kosovars and Estonians are the most likely to be victimised in the building trade.

Pohjola inspected the work agreements of some 500 foreign labourers in Vaasa province last year. He found that only ten percent held contracts that could stand the light of day.

“The biggest problem was underpayment. There's also a lot of unpaid overtime. Inhumane work and housing conditions are also up.”

Raija Kuusisto of PAM’s Ostrobothnia office says the union's field representatives have come across cases of human trafficking in Ostrobothnia.

"There have been cases where foreigners have been forced to work overtime under the threat of being dismissed if they refuse," explained Marja Salmivuori, regional manager of PAM's Vaasa office.

Officials hope a new tax number system being introduced in March will help combat the grey economy in the construction sector. As of next month, construction workers will need to wear a badge featuring their own personal Taxpayer identification Number (TIN) to gain access to building sites.