During the 1990s the number of unauthorized migrant workers increased in Sweden. The Building Workers’ Union (BWU) reacted restrictively to this change. The political objective of the BWU was to preserve the existing institutions in immigration policy. To achieve this end, the Union cooperated with the police to detect unauthorized migrants. The Union became in fact an integral part of the internal migration control that the police performed. The restrictive reaction of the Union created the “illegal” migrant in the construction sector as a political problem in Sweden. This political problem did not exist in Sweden before the 1990s.