A federal judge appointed by President George W. Bush struck down on Monday a key provision of President Barack Obama's health reforms, declaring unconstitutional the mandate that every American purchase insurance.

In a suit filed by Virginia's Republican Attorney General Ken Cuccinelli, US District Court Judge Henry E. Hudson agreed that under the commerce clause, the requirement for citizens to purchase a service did not pass muster of law. The state of Virginia recently passed a law which blocks government from ordering citizens to buy insurance.

The case was widely seen as one which would end up before the US Supreme Court.

Two other federal court judges -- in Virginia and Michigan -- have recently upheld the health insurance mandate.

Republicans were expected to seize upon Monday's ruling as they prepare to take control of the US House of Representatives, where they plan to force a government shutdown, among other parliamentary tactics, to fight the president's agenda.

The White House defended the contitutionality of the insurance mandate and announced its intention to appeal the ruling.

"We disagree with the ruling issued today in Virginia and the Department of Justice is considering its appeal options," wrote Stephanie Cutter, Assistant to the President, on the official White House blog.

"History and the facts are on our side.  Similar legal challenges to major new laws -- including the Social Security Act, the Civil Rights Act, and the Voting Rights Act -- were all filed and all failed.  Contrary to what opponents argue the new law falls well within Congress’s power to regulate economic activity under the Commerce Clause, the Necessary and Proper Clause, and the General Welfare Clause."

The administration had expected to lose before Judge Hudson, according to the Associated Press, but the ruling may not actually be a blow to the policy since the mandate does not take effect until 2014.

Another lawsuit, filed in Florida by 20 states attorneys general, also sought to challenge the health reform laws. It was to be heard in Pensacola by US District Judge Roger Vinson, a Republican appointee.

This story has been updated to include the White House's response.