A report by Human Rights Watch decries what it calls the failure of the Saudi justice system to provide redress.
It speaks of workers who face torture, forced confessions and unfair trials when they are accused of crimes.
But the Saudi embassy in Washington said the report "grossly exaggerates" a few instances of abuse.
"The kingdom... takes the issue of human rights very seriously and we continue to make progress in this regard," it said in a statement.
The 135-page report by the New-York based group catalogues abuses it says are suffered by a predominantly Asian labour force that makes up more than one third of the kingdom's population.
"Migrant workers in the purportedly modern society that the kingdom has become continue to suffer extreme forms of labour exploitation that sometimes rise to slavery-like conditions," it says.
Läs mer: BBC