A protester holds a placard during a protest against Arizona Senate Bill 1070 on April 25 outside of the US Supreme Court in Washington, DC. The Supreme Court began reviewing Arizona's controversial law, which empowers Arizona police officers to stop and demand immigration documents of anyone suspected of being an illegal immigrant.

The Supreme Court ruled on Arizona's immigration law on Monday, striking down key provisions while upholding one of the most controversial measures, according to Reuters.

Justice Anthony Kennedy wrote the opinion that said the controversial "show me your papers" provision, which requires police officers to check the immigration status of the people they stop, said the Associated Press. The court unanimously voted on allowing the status check to go forward.

Here is a breakdown of what was upheld in Arizona's S.B. 1070 and what was struck down, according to MSNBC:

- STRUCK DOWN: A portion of the law which made it a crime for an illegal immigrant to work or seek work in Arizona.

- STRUCK DOWN: A portion of the law which authorized police officers to arrest people on suspicion that they were illegal immigrants.

- STRUCK DOWN: A portion of the law requiring immigrants to register with the federal government.

- UPHELD: A portion of the law requiring police to check the immigration status of someone suspected of being an illegal immigrant.

According to Politico, the justices said the upheld "stop and check" provision did not violate the Constitution or infringe upon the federal government's powers to enforce immigration, but it could still be subject to additional legal challenges once that part of the law takes effect.

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President Barack Obama said in a statement that he was pleased with the court's decision to strike down key provisions of the law. He said, "A patchwork of state laws is not a solution to our broken immigration system - it's part of the problem."

Obama also expressed concern over the remaining provision, saying, "No American should ever live under a cloud of suspicion just because of what they look like." He continued, "Going forward, we must ensure that Arizona law enforcement officials do not enforce this law in a manner that undermines the civil rights of Americans, as the Court’s decision recognizes.

Arizona Gov. Jan Brewer, a Republican, also celebrated the ruling, saying in a statement, "Today’s decision by the US Supreme Court is a victory for the rule of law. It is also a victory for the 10th Amendment and all Americans who believe in the inherent right and responsibility of states to defend their citizens," according to Politico.

Arizona's immigration law seeks to control illegal immigration by "attrition by enforcement" according to Time. It aims to make illegal immigrants leave the country by enforcing criminal laws against illegal immigration.

Supporters of the law claim it is necessary because the federal government has not done enough to enforce immigration laws, while critics argue that it will hurt innocent individuals, including children, said Time.

Republican presidential candidate Mitt Romney said on Monday, "Today's decision underscores the need for a president who will lead on this critical issue and work in a bipartisan fashion to pursue a national immigration strategy," according to Reuters.

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The Supreme Court's ruling comes just a week after President Obama announced a major shift in immigration policy, aiming to ease restrictions on young people who came to the country illegally as children.

The administration opposed the Arizona law and filed similar suits against state laws in Alabama, South Carolina and Utah, according to Politico.

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