WASHINGTON - A sharply divided US Supreme Court on Thursday upheld the centerpiece of US 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.Critics of the law have said it meddles too much in the lives of individuals and in the business of the states.Twenty-six of the 50 US states and a small business trade group challenged the law in court. The Supreme Court in March heard three days of historic arguments over the law's fate.The court's ruling on the law could figure prominently in the run-up to the November 6 election in which Obama seeks a second four-year term against Republican challenger Mitt Romney, who opposed the law."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.The 2010 law, which constitutes the $2.6 trillion US healthcare system's biggest overhaul in nearly 50 years, sought to provide health insurance to more than 30 million previously uninsured Americans and to slow down soaring medical costs.