San Francisco Mayor Gavin Newsom announced today a moratorium on official city travel to Arizona after the state enacted a controversial new immigration law that directs local police to arrest those suspected of being in the country illegally.

The ban on city employee travel to Arizona takes effect immediately, although there are some exceptions, including for law enforcement officials investigating a crime, officials said. It's unclear how many planned trips by city workers will be curtailed.

The move comes amid a cascade of criticism of Arizona's law, which has been denounced by civil rights groups, some police officials and President Obama, who said it threatens to "undermine basic notions of fairness that we cherish as Americans." Legal challenges are being weighed to overturn it.