The US Supreme Court opened blockbuster hearings Monday on President Barack Obama\'s signature health care reform law, a case with huge implications for the nation and the 2012 elections. As the nine justices took their seats in a packed courtroom, hundreds of people were gathered outside, some chanting and marching for and against the Affordable Care Act, sometimes referred to -- usually by detractors -- as \"Obamacare.\" The law has been polarizing for the United States: it would provide health insurance to some 32 million Americans lacking coverage, a major social accomplishment for some, but also would force people to buy insurance -- an intrusion into civil liberties for others. The justices have set aside an unprecedented three days to hear arguments from lawyers representing the government and 26 states who are challenging the law\'s constitutionality. Monday\'s 90 minute hearing is devoted to the narrow question of whether the court has jurisdiction to hear the case before the law has fully gone into effect. A ruling is not expected until June, but if the court decides it does not have jurisdiction, any action on the law would be set aside at least until 2015. The government and the states both agree that the court does have jurisdiction, but the court has designated its own lawyer to argue that it does not. The law\'s most controversial provision -- the so-called \"individual mandate\" requiring all Americans to buy insurance from 2014 or pay a fine -- is to be taken up Tuesday. The top US court has set aside six hours for oral arguments in the case, the longest in the past 45 years. Hearings typically last only about an hour. Both supporters and opponents of the Affordable Care Act have been holding demonstrations to make their voices heard.  \"It\'s health care for everybody. It\'s very important,\" said Jasper Johnson, a 26-year-old computer technician who came from San Francisco, and was among the handful of people camping out since Friday for the few seats set aside for the public to watch the start of the proceedings. \"I\'m here not only for myself but for the economy as a whole.\" But many Republicans oppose the measure, with frontrunning White House hopeful Mitt Romney calling the law an \"unfolding disaster for the American economy.\" His Republican rival, Rick Santorum, planned to make an appearance outside the court after Monday\'s hearing. The ruling could have enormous political ramifications, analysts say, especially if the court strikes down part or all of the reform. \"If the law is struck down, then the administration\'s signature achievement is gone,\" Ilya Shapiro, with the conservative publican policy foundation the Cato Institute, told AFP. The law, enacted in 2010 but which will not come fully into force until 2014, is Obama\'s greatest accomplishment, realizing a long-held dream of generations of Democrats. But Republicans seeking to thwart Obama\'s bid for a second term in the White House see it as an assault on individual liberties, and have vowed to repeal it if elected in the November presidential elections. The main controversy focuses on a measure that requires all Americans to purchase personal health insurance from 2014 or face fines. \"If they can force you to buy health insurance, they can force you to buy a car, asparagus, a gym membership,\" said Kenneth Cuccinelli, attorney general of Virginia, one of 26 states seeking to overturn the law. Other provisions bar insurance companies from refusing to insure people with pre-existing or chronic conditions, who are often now rejected for coverage or forced to pay exorbitant premiums. The companies must also provide certain kinds of coverage that previously were excluded, such as contraception. Opponents argue Congress exceeded its constitutional authority by approving the law. The US Justice Department has hit back arguing the law is within the authority of Congress to regulate commerce and to tax citizens. Senior White House adviser David Plouffe said the government\'s solicitor general, Donald Verrilli, \"is going to put forward a very powerful case for why this law is constitutional and why it\'s important.\" Backers say Americans who lack health care are less productive and often push their unpaid health bills onto taxpayers, who are forced to subsidize emergency room visits. Paul Clement, a former solicitor general who will argue the other side for the 26 states challenging the law, says he will argue it is unprecedented and an \"imposition\" on citizens. Among the nine Supreme Court justices, five were appointed by Republican presidents and four by Democrats.