Increasing numbers of migrant workers have complained of low pay, long hours and substandard accommodation, according to Citizens Advice Scotland.
Migrant workers have entered the job market across Scotland
The agency said the problems were compounded by language issues and a lack of knowledge of basic rights.
The warning came as a Scottish Executive guide is published to help Polish workers settle into communities.
Since European enlargement in 2004, many more workers are now coming to Scotland to take up employment.
They have been filling gaps, particularly in the hospitality and food processing sectors, but also in jobs ranging from bus drivers to dentists.
CAS said bureaux across Scotland were hearing reports of exploitative employers and employment agencies paying below the national minimum wage and making illegal deductions.
Other problems included not getting statutory sick pay or holidays and workers living in overcrowded caravans.
Because accommodation has often been arranged by recruitment agencies, many migrants feared that complaining would lead to dismissal and homelessness.
Kaliani Lyle, chief executive of CAS, said: "Workers have told bureaux of being given false expectations or wrong information about their employment prospects while still in their countries of origin.
"Once in the UK, however, their options for complaining are few, as losing their job means having to return to their own country unless further work becomes available."
She added that without adequate advice people may be deterred from contributing fully to the executive's Fresh Talent drive to boost population and economic growth.
Some workers also reported difficulties in opening bank accounts, obtaining National Insurance numbers and getting work permits.
Initiatives set up by CAS include the Lochaber Migrant Worker Advice Project, which has produced a welcome pack in a number of different languages.
Meanwhile, Finance Minister Tom McCabe is in Warsaw trying to attract more Polish workers to Scotland as part of the Fresh Talent drive, which the executive said had been a success.
The minister stressed the close links between the two countries, with many Polish veterans adopting Scotland as their home after 1945.
Mr McCabe said: "It is no surprise that our Fresh Talent initiative has had an impact in Poland.
First Minister Jack McConnell has driven efforts to attract foreign workers
"In the past two years, around 20,000 Poles have come to work in Scotland.
"However, promoting Scotland in Poland and attracting people to come to Scotland is not enough.
"We must support individuals to integrate and settle into Scottish life once they arrive."
Scottish National Party enterprise spokesman Jim Mather welcomed the contribution made by the "many bright hard-working Poles" in Scotland.
However, he added: "An information guide, though it may be useful, is not going to create the economic climate in Scotland needed to attract more immigrants and reverse our population decline."
Also on Monday, Health Minister Andy Kerr is in Dumfries and Galloway to see the impact of recently recruited Polish dentists.
The Fresh Talent initiative aims to help tackle Scotland's ageing population by attracting people to live, work and study in Scotland.