Vinson ruled that the law’s requirement that nearly all Americans purchase health insurance coverage is not within the legal bounds of Congress’s power under the Commerce Clause. (Read Judge Roger Vinson Healthcare Ruling [PDF])

Because the provision is instrumental to the rest of the law, he declared the entire law unconstitutional. The law also doesn’t have a severability clause, a common legal phrase that prevents courts from striking down a whole law because one piece has been found to be illegal.

“Because the individual mandate is unconstitutional and not severable, the entire act must be declared void,” he wrote in his 78-page ruling. “This has been a difficult decision to reach, and I am aware that it will have indeterminable implications.”

Because several district courts have ruled differently on the issue, the ruling is unlikely to have an immediate impact on implementing the law, but it is expected to increase the partisan, political rhetoric for and against health reform. The U.S. Department of Justice said it plans to appeal the decision and is considering whether it needs to ask for a stay.

“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,” DOJ spokeswoman Tracy Schmaler said in a statement.

The Obama administration dubbed the ruling “well outside of the mainstream judicial opinion” and said implementation of the law won’t change.

“I don’t think you should view this as the opening of the government shutting down the implementation effort,” a senior administration official said.

The Pensacola case is now likely headed for the 11th Circuit Court of Appeals, which is based in Atlanta and considered of one of the most conservativ

e circuit courts. Other reform-related lawsuits are traveling through the Fourth and Sixth Circuits.

So far, four district court judges have ruled on the merits of the health reform law. Underscoring the political subtext of the legal debate, the judges have ruled along partisan lines.

Two judges, both appointed by Republican presidents, have struck down the law or its main provision. Two other judges appointed by Democrats have upheld the legislation as constitutional.

A dozen more legal challenges to reform have been knocked out of court on procedural grounds.

But the Florida lawsuit is the most high-profile and politically charged lawsuit against reform. It was brought by 26 states and the National Federation of Independent Business. In addition, several members of Congress signed amicus briefs in support or opposition.

The issue is widely expected to eventually reach the U.S. Supreme Court.

Senate Majority Whip Dick Durbin (D-Ill.) has called a hearing on the constitutionality of the law to be held on Wednesday before the full Judiciary Committee. House Judiciary Committee Chairman Lamar Smith (R-Texas) has a similar hearing scheduled for next month.

Proponents of health reform argue that the so-called individual mandate is pivotal to delivering key insurance industry reforms in the law, such as a ban on denying patients over pre-existing conditions. It’s due to go into effect in 2014.

They immediately tried to downplay the decision, arguing that it is a display of extreme judicial activism.

“Judge Vinson’s decision is radical judicial activism run amok, and it will undoubtedly be reversed on appeal,” said Ron Pollack, executive director of Families USA, an advocacy group that supports health reform. “The decision flies in the face of three other decisions, contradicts decades of legal precedent, and could jeopardize families’ health care security.”

“I remember when Republicans thought that activist judges shouldn’t legislate from the bench,” said Rep. Pete Stark (D-Calif.). “Several other judges across the country have already ruled that the health reform law is constitutional, a viewpoint that will win the day at the end of all this partisan posturing.”

Republicans praised the ruling, arguing that the courts have finally recognized their long-held contention the law is not legally sound.

“This ruling confirms what Americans have been saying for months,” said Senate Minority Leader Sen. Mitch McConnell (R-Ky.). “The health spending bill is a massive overreach and Democrats ‘exceeded the bounds’ of congressional authority under the Constitution in passing the law with the individual mandate.”

The key legal question in the numerous lawsuits over the individual mandate has come down to whether the Constitution’s Commerce Clause gives Congress the power to regulate the decision to buy insurance.

The states and NFIB contended during oral arguments in December that the Congress has no constitutional right to force Americans buy insurance coverage. They said that while Congress is authorized to regulate activity, they can’t regulate inactivity — or not buying insurance.

The federal government argued that Congress has a right to regulate the insurance market because it is unique — it’s fair to assume that every single person will need health care at some point in his or her life. If they’re not insured, their costs will have to be picked up by other consumers, driving up rates for everyone and putting them in the insurance market whether they plan to or not.

During oral arguments in December, Vinson suggested that it would be a “giant leap” for the Supreme Court to say a decision not to buy insurance is the same as activity. He questioned whether Congress could require people to buy other products if they have a positive impact.

Could they “mandate everybody has to buy a certain amount of broccoli?” Vinson questioned, comparing the positive impact both could have on health.

The federal government argued that health insurance and health care are unique markets and that Congress has the power to regulate them.

“It’s not shoes. It’s not broccoli,” said Ian Gershengorn, arguing for the federal government. “Health insurance is a product that is a financing mechanism.”

It’s the lack of the severability clause that could make the legal challenges more complicated. The clause typically prevents an entire law from being voided over just one provision.

It likely wasn’t included in the Senate bill that eventually became law because the Senate legislation was never expected to be final. When Sen. Scott Brown (R-Mass.) was elected in January 2010, Democrats were forced to let the legislation pass the House with only the alterations that were allowed in the technical reconciliation process. Proponents of reform have frequently argued that the missing severability clause shouldn’t hold up the whole law.

The states and NFIB also argued that the law’s mandatory expansion of the Medicaid program commandeered the states into federal service. But Vinson ruled against the states on the point.