The U.S. Supreme Court on Monday struck down most of Arizona's immigration law but decided one of its most controversial provisions can be enforced.

The high court's ruling found that immigration enforcement should mainly be left up to the federal government and not states.

However, in a unanimous vote, the so-called "check your papers" provision - requiring police officers to check the immigration status of anyone they suspect is in the country illegally - was upheld.

For now, Arizona can continue to enforce that part of the law, though the court's justices say it could be subject to additional legal challenges.

President Obama says although he is pleased with the overall tone struck by the justices, the fact that those checks can continue has him "concerned."

In a statement, the president went on to say "What this decision makes unmistakably clear is that Congress must act on comprehensive immigration reform. A patchwork of state laws is not a solution to our broken immigration system - it’s part of the problem."

Some local advocates share the same concerns.

“The Supreme Court decided today that it is OK to ask, to terrorize our communities and ask them for papers,” said Ana Maria Archila of Make the Road New York.

"This decision is a step back for civil rights in the USA and we will fight it," said Center for Community Change Executive Director Deepak Bahargava.

Other parts of the law made it a crime for immigrants without work permits to seek work and made it a crime for immigrants to fail to carry registration documents.

The Obama administration had challenged Arizona's law, arguing that immigration enforcement should fall under the jurisdiction of the federal government.

"I would have liked to see where we have the authority to arrest illegal aliens just by being here illegally and book them into our jail but that's not going to happen," said Maricopa County Sheriff Joe Arpaio.

Arizona Governor Jan Brewer claimed victory and took a swipe at President Obama.

“Instead of devoting resources to suing states like Arizona, the federal government should have spent time, money and energy on fixing the problem,” she said.

The decision comes on the same day the court was expected to rule on whether President Barack Obama’s Affordable Care Act is constitutional.

A decision could still come before the end of the week.

At the heart of the matter is the individual mandate.

That's the part of the Affordable Care Act that requires the vast majority of Americans acquire health insurance, or pay a penalty.

A total of 26 states have filed suit calling it unconstitutional.

Supporters argue the law provides coverage for millions who didn't have it before, adding that Congress has the authority to regulate commerce.