"We must not forget those who are less fortunate in times of prosperity," she said. "We must not turn our backs on people because it is not fashionable to support them.We must not forget those who are less fortunate than ourselves."
Ms Flanagan said her own experience as an undocumented immigrant in the US had showed her how simple it was to fall out of status.
"But I was lucky," she said. "People were able to help me get back on my feet. Today's undocumented Irish are not so lucky."
She urged the Irish Americans present to contact their legislators to ask for help for the undocumented Irish. "It is up to us, Irish Americans, to reach out to our leaders."
Ms Flanagan has been a long-time supporter of the campaign for immigration reform in the US."Over the years, when asked, I have lent my name and whatever support I could to a variety of organisations in southern California which have championed sanctuary and the rights of immigrants who come largely from Central America. Their struggle is not easy and the bias against them is horrendous," she said.
Earlier this year, the Emmy-winning Irish actress pulled out of the U.S. Ireland Alliance pre-Oscar awards bash over comments made by its president Trina Vargo which criticised the campaign for the undocumented Irish.
Ms Flanagan said she refused to be "honored" by an organization that appeared to "castigate or shame" the "most vulnerable of (her) countrymen".