There's an interesting mention in a New York Times article which says a legal database search showed it was the first time the Supreme Court used "undocumented immigrant" in an opinion, though it has used "illegal immigrant" in a dozen decisions.
The "undocumented" vs. "illegal" debate is never-ending. Here's an earlier post from our immigration editor that explores the debate over such usage in the media. It's also an issue that local governments and the court system have struggled with for years.
Justice Sotomayor's choice of words is being hailed by immigrant advocates. On ImmigrationProf Blog, University of California law professor Kevin Johnson wrote that with her first written Supreme Court decision - which by the way focused on a civil procedure issue - the new justice "already has made a difference"
Johnson writes that "the choice of terminology -- aliens, illegal aliens, illegal immigrants, undocumented immigrants, people -- matters in the discourse over immigration. Consequently, by employing a more neutral term, Justice Sotomayor has added significantly to the Supreme Court's dialogue on immigration, which is likely to be with us for the foreseeable future."
The usage is bound to cause some backlash in some circles. We'll keep you posted.