Mexico has issued a warning to its citizens that travel to Arizona could result in harassment and questioning without further cause. Meanwhile, the city of San Francisco has banned its workers from traveling to Arizona, effective immediately, including law enforcement investigating crime. Both measures are in response to the controversial immigration legislation just signed by the state's governor; the law requires police to check the citizenship of anyone they suspect is in the country illegally. President Obama and Homeland Security Secretary Janet Napolitano, among others, have criticized the law. Many have threatened boycotts, and, in fact, an Arizona congressman has even encouraged one.