A lack of legal protection for migrant workers who arrive in the UK is giving the green light to unscrupulous employers to exploit them, according to the TUC.
The report by the union body - titled "Overworked, underpaid and over here" - lists a catalogue of employer abuse.
In particular, the report claims migrant workers have to put up with low levels of pay, poor housing and long hours as employers take advantage of their often shaky command of the English language.
As a result the TUC has called on the UK government to sign up to the UN Convention on the Rights of Migrant Workers and prosecute employers who take advantage.
The number of migrant workers as a proportion of the UK workforce has increased by nearly a third since 1995.
But the TUC insists that this only represents the tip of the iceberg as many migrant workers work in the UK illegally.
Foreign students - who can work up to 20 hours a week during term time - make up the largest proportion of migrant workers.
The report highlights a catch-22 situation encountered by many migrant workers.
Poorly treated workers, including migrant, have the right to take their employers to an industrial tribunal, but by doing so they could lose their job and as a consequence their right to stay in the UK.
"Most migrant workers only stay for short periods, and their precarious legal status means many end up working incredibly long hours for not much pay, in jobs that UK workers wouldn't want to do," TUC general secretary Brendan Barber said.