DETROIT – A federal judge on Thursday upheld the authority of the federal government to require everyone to have health insurance, dealing a setback to groups seeking to block the new national health care plan.

The ruling came in a lawsuit filed in Michigan by a Christian legal group and four people who claimed lawmakers exceeded their power under the Constitution’s commerce clause, which authorizes Congress to regulate trade.

But Judge George Caram Steeh in Detroit said the mandate to get insurance by 2014 and the financial penalty for skipping coverage are legal.

“Without the minimum coverage provision, there would be an incentive for some individuals to wait to purchase health insurance until they needed care, knowing that insurance would be available at all times,” the judge said. Julian Davis Mortenson, a University of Michigan law professor and former U.S. Supreme Court law clerk, said the decision affects only the parties in the lawsuit and is not binding on any other federal judges hearing challenges.

Nonetheless, the Justice Department hailed Steeh’s opinion as the first time a “court has considered the merits of any challenge to this law.”

Robert Muise of the Thomas More Law Center in Ann Arbor, Mich., which filed the case, said he would take it to a federal appeals court in Cincinnati. In Florida, a federal judge is overseeing a lawsuit filed by 20 states. They, too, say the law is unconstitutional and claim it would force states to absorb higher Medicaid costs.