PHOENIX — Groups opposing Arizona's immigration enforcement law are trying to chip away at a section of the statute that bans the blocking of traffic when people seek or offer day-labor services on streets.

The Mexican American Legal Defense and Educational Fund and other opponents asked a federal judge on Friday to block enforcement of the provision. They argue that it unconstitutionally restricts free speech rights and they say the state can't justify a statewide ban based on scattered instances of solicitations creating traffic problems in Phoenix.

The ban was among a handful of provisions in the law that were allowed to take effect after a July 2010 decision by U.S. District Judge Susan Bolton blocked enforcement of the law's more controversial elements.