The Government is to launch a research project to try to determine the number of people working illegally in Ireland following rising concern over the number of undocumented workers here.
Minister for Enterprise and Employment Micheál Martin said there were currently no hard figures and that he and Minister for Justice Brian Lenihan were going to tackle the issue.
Groups such as the Migrant Rights Centre Ireland and the Immigrant Council of Ireland have warned that large numbers of migrant workers who came here legally have become undocumented for reasons beyond their control.
Such workers are often vulnerable to exploitation and mistreatment.
For example, the migrant rights centre estimates that of 1,000 migrant workers who sought its support last year, about one quarter had become undocumented. Almost all had entered the country legally on a work permit.
Mr Martin said it was important to find out why people were becoming undocumented and to get a proper estimate of the number of undocumented people here.
"Are they due to non-renewal of work permits, people on student visas disappearing into the ether or people who have come in via holiday visas still being around?
"Our worry from an employment rights perspective is that when you have people that are without status they are very vulnerable to exploitation."
However, Mr Martin said the Government was not talking about an amnesty for those involved.
Jacqueline Healy, Migrant Rights Centre Ireland's acting director, said preliminary findings from its own research indicated that workers were becoming undocumented as a result of exploitation in the workplace, being misled about work permit applications, being trafficked for forced labour or being made redundant.
"Such workers are often prime targets for exploitation as many choose not to come forward to report exploitation," she said.
The group has suggested introducing a "bridging visa" - or temporary permission to remain - for people who have become undocumented for reasons beyond their control.
"We hope that the Government will implement such a response, similar to that being advocated by the Irish Government for undocumented Irish people in the US," Ms Healy said.
Denise Charlton, chief executive of the Immigrant Council of Ireland, said undocumented workers were also less likely to avail of vital services such as healthcare due to fears over their illegal status.
"We have situations where people have long-term illness like cancer or else they are pregnant. They tend to wait to the very last minute to seek assistance."