WASHINGTON - A federal judge in US state of Florida on Monday ruled the healthcare law unconstitutional, dealing a second legal blow to President Obama's signature reform legislation after a Virginian judge stroke down a core provision of the law last month.

US District Judge Roger Vinson ruled that the "individual mandate," which requires almost every American buy health insurance or face a penalty, exceeds the boundaries the Constitution gives the Congress to regulate interstate activities.

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"To now hold that Congress may regulate the so-called 'economic decision' to not purchase a product or service in anticipation of future consumption is a  'bridge too far,' " Vinson wrote in his ruling.  "It is without logical limitation and far exceeds the existing legal boundaries established by Supreme Court precedent."

While Virginian Judge Henry Hudson, the first federal judge to rule against the law, stroke down only the "individual mandate" provision and left the rest of the law in place, Vinson invalidated the entire package.

"Because the individual mandate is unconstitutional and not severable, the entire act must be declared void," Vinson wrote in his ruling. "I must conclude that the individual mandate and the remaining provisions are all inextricably bound together in purpose and must stand or fall as a single unit."

The US Department of Justice said it plans to appeal the decision.

"We strongly disagree with the court' s ruling today and continue to believe -- as other federal courts have found -- that the Affordable Care Act is constitutional," the department spokeswoman Tracy Schmaler said in a statement.

The lawsuit, filed by 26 states and the National Federation of Independent Business, has so far been the most high-profile legal challenge to the law. Altogether, four federal judges have made rulings on the law, with two for it and two against it. The rulings were made completely along the party line. The two judges who ruled in favor of the law were Democratic appointees while the others were Republican appointees.

The White House called the latest ruling "judicial activism" and would not upheld by the Supreme Court, which is expected to make final ruling on this controversial legislation.

"The judge's decision contradicts decades of Supreme Court precedent that support the considered judgment of the democratically elected branches of government that the act's individual responsibility provision is necessary to prevent billions of dollars of cost-shifting every year by individuals without insurance who cannot pay for the health care they obtain," White House adviser Stephanie Cutter wrote in an internet posting.

"We don't believe this kind of judicial activism will be upheld and we are confident that the Affordable Care Act will ultimately be declared constitutional by the courts," he wrote.

The ruling might add new momentum to Republican efforts to repeal the law. Earlier this month, the House of Representatives, which is now controlled by Republicans, passed a bill to repeal the law, but Senate Democrats vowed to block the repeal bill from getting a floor vote in the upper chamber.