Arizona’s extremist immigration law has gone another round in federal court — and lost again. The judge who rejected several of its provisions in 2010 temporarily blocked another section last week, the one making it a crime for day laborers to look for work on the street.

The state had argued that it had restricted day-labor solicitation in the interests of traffic safety. But Judge Susan Bolton of Federal District Court ruled that the plaintiffs challenging the provision on First Amendment grounds were likely to prevail, given that the law seemed written to target particular speech “rather than a broader traffic problem.” She noted that Arizona has traffic laws to prevent dangerous acts by pedestrians and cars.

States and localities have tried for decades to write laws to throw day laborers off the corner and have repeatedly run up against the Constitution. Last fall, the United States Court of Appeals for the Ninth Circuit threw out an antisolicitation ordinance in Redondo Beach, Calif., calling it a “facially unconstitutional restriction on speech,” written so broadly that it could ban sidewalk activities that do not disrupt traffic at all. In February, the Supreme Court wisely refused to reverse the Redondo Beach decision.

In Arizona, as in Redondo Beach, it has been left to judges to protect immigrant laborers when government officials seek to drive them out of sight. Judge Bolton rightly noted that the first section of the Arizona law declares “attrition through enforcement” — the mass expulsion of undocumented immigrants through wide-ranging crackdowns — to be the official policy of state and local government in Arizona. What does that have to do with traffic safety? Nothing, Judge Bolton pointed out, exposing Arizona’s unconstitutional law for what it is.