WASHINGTON (Reuters) - A sharply divided Supreme Court on Thursday upheld the centerpiece of President Barack Obama's signature healthcare overhaul law that requires that most Americans get insurance by 2014 or pay a financial penalty.

"The Affordable Care Act's requirement that certain individuals pay a financial penalty for not obtaining health insurance may reasonably be characterized as a tax," Chief Justice John Roberts wrote for the court's majority in the opinion.

"Because the Constitution permits such a tax, it is not our role to forbid it, or to pass upon its wisdom or fairness," he concluded. The vote was 5-4.

(Reporting by James Vicini; Editing by Will Dunham)