Reports from the New York Times, SCOTUSblog, and MSNBC say that the Supreme Court in a 5-4 vote has upheld the Affordable Care Act.

The law, which has become known as Obamacare, is President Obama’s signature piece of first-term legislation.

The court’s decision appears to interpret the law’s requirement to purchase health insurance as a tax, with the majority opinion written by Chief Justice John Roberts.

The decision is major victory for President Obama and a strong rebuke for Republicans, including presidential hopeful Mitt Romney, who has vowed to strike down the law.