A sweeping new immigration enforcement bill signed into law by the governor of Arizona on Friday has met with immediate opposition from students and others around the nation.

The law, known as SB 1070, has many elements, but its most controversial is a mandate that police officers to detain people they believe to be in the United States illegally.

President Obama on Friday described the law as a threat to “trust between police and our communities” and to “basic notions of fairness that we cherish as Americans.” The Archbishop of Los Angeles has compared the law’s provisions to Nazism.

SB 1070 provoked mass student protests even before it was signed — on Thursday morning more than a thousand Phoenix-area high school students walked out of classes and marched on the state capitol to demand that governor Jan Brewer veto the bill.

Dream Activist, a website by and for students organizing for immigration reform, reports that rallies and vigils were planned for Saturday in California, Florida, Kansas, Massachusetts, Michigan, Minnesota, New York, and Washington DC.

Opponents of the law are using the hashtags #SB1070 and #LegalizeAZ on Twitter.

Update | Add Connecticut to the list of states hosting anti-SB1070 protests — Yale students staged a mock ICE raid on campus on Thursday.