US President Barack Obama has announced an immediate end to the deportation of illegal immigrants who came to the US as children, describing the move as "the right thing to do".
Those aged between 16 and 30 who have lived in the US for five years could now be eligible for work permits.
The move is seen as addressing a key Latino concern in an election year.
But Obama's Republican opponent, Mitt Romney, said it was the wrong way to approach the problem.
Romney said the issue should be dealt with by legislation, rather than an executive order "that can be reversed by subsequent presidents".
The plan, which goes into effect immediately, is expected to affect as many as 800,000 people.