An investigation into the expansion of Sao Paulo international airport found that 111 workers were living in poor accommodation near the building site.
They were approached in poorer states and some had to pay more than $220 (£140) to secure a job, the Labour attorney general’s office says.
The promised wages were $625 a month.
The workers, among them six ethnic Pankaruru indians, were reportedly lured in the country’s north-east with promises of work in Sao Paulo.
However, many were not immediately employed and had to stay in one of 11 makeshift camps near the airport which is being expanded in preparation for next year’s World Cup.
The Labour attorney general’s office says it found the workers living in “conditions analogue to slaves” and has 30 days to present legal action against the contractors.