The Migrants Rights Centre is calling on the Government to introduce a scheme that would allow undocumented people living in Ireland to regularise their situation.
It said Government ministers will spend this weekend lobbying US politicians on behalf of the undocumented Irish in America, while ignoring the plight of undocumented people in Ireland.
Speaking on RTÉ's Morning Ireland, Deputy Director of Migrants Rights Edel McGinley said there are tens of thousands of undocumented people living here.
She said: "We estimate that there is between 26,000-30,000 undocumented people here in Ireland. Many people have been here up to ten, 12, 15 years.
"They are part of communities. They have been working here paying taxes contributing to the economy for a very long time."
Ms McGinley said life for many of them is very difficult and many have not been to see their families in ten to 15 years.
She said they tend to work in less regulated sectors of the economy - restaurants, care in private homes, cleaning and providing maintenance.
They are often exploited by their employers, they have no terms or conditions, no holiday or sick pay and, in some cases, they are paid below the minimum wage.