PHOENIX — A federal judge blocked police in Arizona from enforcing a section of the state’s 2010 immigration enforcement law that prohibited people from blocking traffic when they seek or offer day labor services on streets.

U.S. District Judge Susan Bolton ruled Wednesday that groups seeking to overturn the law will likely prevail in their claim that the day labor rules violate the First Amendment. She rejected arguments by the state that the rules were needed for traffic safety and pointed out that the law, also known as SB1070, says its purpose is to make attrition through enforcement the immigration policy of state and local government agencies.

“This purposes clause applies to all sections of SB1070, and nowhere does it state that a purpose of the statutes and statutory revisions is to enhance traffic safety,” the judge wrote.

The ban was among a handful of provisions in the law that were allowed to take effect after a July 2010 decision by Bolton halted enforcement of other, more controversial elements of the law. The previously blocked portions include a requirement that police, while enforcing other laws, question people’s immigration status if officers suspect they are in the country illegally.

The U.S. Supreme Court has agreed to hear Gov. Jan Brewer’s appeal of Bolton’s decision to put the most contentious elements of the law on hold. Another appeals court has already upheld Bolton’s July 2010 ruling.

Three of the seven challenges to the Arizona law remain alive. No trial date has been scheduled in the three cases.

Some of Arizona’s biggest law enforcement agencies have said in the past that they haven’t made any arrests under the sections of the law that were allowed to take effect.

Brewer said in a statement that she was disappointed with Bolton’s “erroneous decision,” which she said has further eroded the state’s ability to regulate public safety. Also, Wednesday’s ruling is just one more reason to look forward to the Supreme Court’s scheduled consideration of SB1070 in April, she said.

The governor signed the measure into law in the spring of 2010.

Dan Pochoda, legal director for the American Civil Liberties Union of Arizona, one of the group’s representing people who filed the lawsuit, said the judge saw through the government’s ruse that the day labor rules were about traffic safety, when the goal all along was to get at day laborers.

“There are clear laws now that allow any cop to unclog (the streets) well before they had this law,” Pochoda said.

The Mexican American Legal Defense and Educational Fund and other opponents had asked the judge for a preliminary injunction to block enforcement of the day labor rules, arguing they unconstitutionally restrict the free speech rights of people who want to express their need for work.

Brewer’s lawyers had opposed attempts to halt enforcement of the day labor restrictions. They argued the restrictions are meant to confront safety concerns, distractions to drivers, harassment to passers-by, trespassing and damage to property.

Brewer’s lawyers have said day laborers congregate on roadsides in large groups, flagging down vehicles and often swarming those that stop. They also said day laborers in Phoenix and its suburbs of Chandler, Mesa and Fountain Hills leave behind water bottles, food wrappers and other trash.

The judge wrote in her latest ruling Wednesday that the law appears to target particular speech rather than a broader traffic problem. “The adoption of a content-based ban on speech indicates that the Legislature did not draft these provisions after careful evaluation of the burden on free speech,” the judge wrote.

Bolton previously denied an earlier request to block the day labor rules, but opponents were allowed to bring it up again after the 9th Circuit Court of Appeals ruled on a similar issue in September.

The appeals court had suspended a law from Redondo Beach, Calif., that banned day laborers from standing on public sidewalks while soliciting work from motorists. The court ruled the law violated workers’ free speech rights and was so broad that it was illegal for children to shout “car wash” to passing drivers.

The ruling Wednesday still leaves other elements of the law in place, such as minor tweaks to the state’s 2005 immigrant smuggling law and 2007 law prohibiting employers from knowingly hiring illegal immigrants.

Other parts of the law that remain in effect include a prohibition on state and local government agencies from restricting the enforcement of federal immigration law and a ban on state and local agencies from restricting the sharing of information on people’s immigration status for determining eligibility of a public benefit.