"We're talking about human trafficking, plain and simple," Tommy Andersson of GS, the Swedish union of forestry, wood and graphical workers, told Svergies Television (SVT) investigative news programme Uppdrag granskning.
According to a programme to be broadcast on Wednesday night, Swedish forestry giants SCA and Holmen hire agents to recruit migrant workers from Cameroon, luring them to Sweden with false promises of good pay.
The practice has been going on for the past two years and involves sending documents to the Swedish Migration Board (Migrationsverket) indicating the workers will earn 18,500 kronor ($2,825) per month and which have been approved by the union.
But the promised wages appear only to exist on paper, according to Uppdrag granskning.
When the Cameroonian workers arrive in the forests of northern Sweden, they are forced to carry out piece work for much lower pay.
They were also forced to pay hefty fees to the agents before being allowed to start working in the first place.
When some of the workers complained, the agent threatened to burn down their homes back in Cameroon, according to the SVT report.
Six months after the end of the planting season, many of the Cameroonian workers remain in Sweden as undocumented immigrants.
They lack housing, money, and work and are afraid to return home because they lack money to pay off the debts incurred to make the journey to Sweden.
The Swedish forestry firms told Uppdrag granskning they were also "duped" by the recruiting agents, but claim they have no obligation to help the workers with their predicament.
"We have a contract agreement with businesslike provisions with the agent. We don't have any agreement which involves any responsibility for their staff," Jan Sandström, regional manager with Holmen AB, told SVT.