A second US federal judge Monday declared President Barack Obama's health care law unconstitutional, sparking a fierce new showdown with Republicans who vow to repeal the historic reform act.
The Obama administration immediately pledged to appeal and branded the ruling by a Florida judge as an "outlier" from the judicial mainstream, warning that health care costs would soar if it was allowed to stand.
But Republicans crowed that the ruling was one step closer to the outright repeal of a law that has been a Democratic dream for decades but that conservatives say will explode the deficit and kill jobs.
US District Judge Roger Vinson said a key provision of the law known as the "individual mandate" exceeds Congress's regulatory powers by requiring Americans to either purchase health insurance by 2014 or pay a fine.
"Because the individual mandate is unconstitutional and not severable, the entire act must be declared void," Vinson said in his ruling, the latest step of a twisting legal battle likely to end up in the US Supreme Court.
"This has been a difficult decision to reach, and I am aware that it will have indeterminable implications."
Vinson agreed with governors and attorneys general from 26 US states that consider the provision unconstitutional.
But the Justice Department quickly said it would appeal Vinson's ruling, and consider all options -- including a stay of the verdict pending appeal -- to ensure the health care law can go into force.
The health care law, which passed last year, is the most sweeping piece of social legislation since the 1960s, reins in insurance company abuses and brings America as close as it has ever been to universal coverage.
"Today's ruling... is a plain case of judicial overreaching," Stephanie Cutter, a senior political assistant to Obama, said in a White House blog post.
"The judge's decision puts all of the new benefits, cost savings and patient protections that were included in the law at risk."
In December, Judge Henry Hudson of the Eastern District Court in Richmond, Virginia, found that the mandate usurps federal authority and violates the Commerce Clause, a key component of the US Constitution.
Some 12 federal judges have already struck down challenges to the law, and two have upheld the legislation.
Republicans pounced on the latest ruling, seeking fuel for their campaign to overturn the reform -- a vain hope for now, as Obama could wield a presidential veto in the unlikely event a repeal law cleared Congress.
Senate Republican Minority Leader Mitch McConnell said the court's decision proved the health care law was a "massive overreach" and exceeded congressional authority.
"We should repeal this health spending bill and replace it with commonsense reforms that will actually lower costs, prevent unsustainable entitlement promises and make it easier for employers to start hiring again," he added.
Republican National Committee Chairman Reince Priebus called the ruling a "major victory for the American people and job-creators all across the country."
Obama's Republican foes have claimed the health care law includes rationing for end of life care, would add to the massive deficit and will kill jobs as employers struggle to pay for what they say will be rising premiums.
The new Republican-led House of Representatives has already voted to repeal the health reform law, which reins in insurance firms and seeks to offer near-universal care to Americans for the first time.
Obama said in his State of the Union address earlier this month that he was "eager" to work with Republicans to make small improvements in the law but was not willing to consider a complete repeal.
Opinion polls have found the US public deeply divided over the health law, with roughly one in five in favor of outright repeal and the rest divided between strengthening the law and rolling back parts of it.