The individual health insurance mandate is constitutional, the Supreme Court ruled Thursday, upholding the central provision of President Barack Obama's signature Affordable Care Act.

The 5-4 majority opinion, written by Chief Justice John Roberts, upheld the mandate as a tax, although concluded it was not valid as an exercise of Congress' commerce clause power. Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan joined in the majority.