New York Mayor Bill de Blasio has said the city would give undocumented immigrants identity papers to allow them to live more normal lives.
"To all of my fellow New Yorkers who are undocumented, I say: New York City is your home too, and we will not force any of our residents to live their lives in the shadows," Mr de Blasio said in a speech at Queens College.
The aim of the initiative is to ensure that undocumented residents are able to do things such as open bank accounts, sign leases and gain access to basic services.
"We will protect the almost half-million undocumented New Yorkers whose voices too often go unheard," Mr de Blasio said.
Mr de Blasio was elected mayor in November with the massive support of the city's Hispanic and black communities, who responded to his promise to fight to close a growing gap between rich and poor.
He took office on 1 January, succeeding billionaire Michael Bloomberg, who was mayor for 12 years.
Mr de Blasio will be the first New York mayor in two decades not to take part in the St Patrick's Day parade along Fifth Avenue because of a row over gay rights.