(CNN) -- A Virginia federal judge on Monday found a key part of President Barack Obama's sweeping health care reform law unconstitutional, setting the stage for a protracted legal struggle likely to wind up in the Supreme Court.

U.S. District Judge Henry Hudson struck down the "individual mandate" requiring most Americans to purchase health insurance by 2014. The Justice Department is expected to challenge the judge's findings in a federal appeals court.

Hudson's opinion contradicts other court rulings finding the mandate constitutionally permissible.

"An individual's personal decision to purchase -- or decline purchase -- (of) health insurance from a private provider is beyond the historical reach of the U.S. Constitution," Hudson wrote, also stating that "no specifically articulated constitutional authority exists to mandate the purchase of health insurance."

"Despite the laudable intentions of Congress in enacting a comprehensive and transformative health care regime, the legislative process must still operate within constitutional bounds," Hudson added. "Salutatory goals and creative drafting have never been sufficient to offset an absence of enumerated powers."

A federal judge in Virginia ruled in favor of the administration earlier this month over the purchase requirement issue, mirroring conclusions reached by a judge in Michigan back in October.

Virginia officials had argued that the Constitution's Commerce Clause does not give the government the authority to force Americans to purchase a commercial product -- like health insurance -- that they may not want or need. They equated such a requirement to a burdensome regulation of "inactivity."

Virginia is one of the few states in the country with a specific law saying residents cannot be forced to buy insurance.

"I am gratified we prevailed," said Virginia Attorney General Ken Cuccinelli, a conservative Republican elected in 2009. "This won't be the final round, as this will ultimately be decided by the Supreme Court, but today is a critical milestone in the protection of the Constitution."

Incoming House Majority Leader Eric Cantor, R-Virginia, urged Obama and Attorney General Eric Holder to request an expedited appeal to the Supreme Court.

"Ultimately, we must ensure that no American will be forced by the federal government to purchase health insurance they may not need, want, or be able to afford," Cantor said. "In this challenging environment, we must not burden our states, employers, and families with the costs and uncertainty created by this unconstitutional law, and we must take all steps to resolve this issue immediately."

White House Press Secretary Robert Gibbs told reporters the decision by Hudson -- a 2002 George W. Bush appointee -- was not "a surprise to anybody."

"We disagree with the ruling," he said. Among other things, the provisions requiring everyone to buy insurance allow the government to "finally address the lingering discrimination" against individuals with pre-existing conditions, he said.

"When all the legal wrangling is said and done ... this is something that will be upheld," he predicted. "I think we have a good argument. I think the merits of the case are strong."

A Justice Department spokeswoman also expressed confidence the administration will eventually win the legal fight.

"We are disappointed in today's ruling but continue to believe -- as other federal courts in Virginia and Michigan have found -- that (the law) is constitutional," Tracy Schmaler said. "There is clear and well-established legal precedent that Congress acted within its constitutional authority in passing this law and we are confident that we will ultimately prevail."

Obama signed the Patient Protection and Affordable Care Act in March, after promoting Democratic-led health reform efforts for months after taking office. The law is widely considered to be the signature legislative accomplishment of the president's first two years in office.

Among other things, the measure was designed to help millions of uninsured and underinsured Americans receive adequate and affordable health care through a series of government-imposed mandates and subsidies. The federal government stated in court briefs that last year, 45 million Americans were without health insurance, roughly 15 percent of the country's population.

Critics have equated the measure to socialized medicine, fearing that a bloated government bureaucracy will result in higher taxes and diminished health care services. About two dozen challenges have been filed in federal courts nationwide.

On November 8, the Supreme Court rejected the first constitutional challenge to the health care reform effort, resisting a California conservative group's appeal. The justices refused to get involved at a relatively early stage of the legal process.

The high court rarely accepts cases before they have been thoroughly reviewed by lower courts.

Legal experts say they expect several of the larger issues in the health care debate to ultimately end up before the Supreme Court. A review from the high court may not happen, however, for at least a year or two.

The highest-profile lawsuit may come from Florida. State officials there have objected not only to the individual coverage mandate but also to a requirement forcing states to expand Medicaid. Florida's litigation is supported by 19 other states: Alabama, Alaska, Arizona, Colorado, Georgia, Idaho, Indiana, Louisiana, Michigan, Mississippi, Nebraska, Nevada, North and South Dakota, Pennsylvania, South Carolina, Texas, Utah and Washington.

Health care reform, a top Democratic priority since the Truman administration, passed the current Congress in a series of virtual party-line votes. Opponents derisively labeled the measure "Obamacare." Republican leaders, who captured the House of Representatives in the midterm elections, have vowed to overturn or severely trim the law.

"While this court's decision may set the initial judicial course of this case, it will certainly not be the final word," the 63-year-old Hudson wrote in October.

The case decided Monday is Virginia v. Sebelius (3:10-cv-00188).

CNN's Alan Silverleib contributed to this report.