A U.S. judge on Thursday handed a victory to congressional Republicans who challenged President Barack Obama's signature health care law, ruling that his administration overstepped its constitutional powers relating to government spending.

U.S. District Judge Rosemary Collyer, based in Washington, ruled that the administration cannot spend billions of dollars in federal funds to provide subsidies under the law known as Obamacare to private insurers without the approval of Congress.

At issue in the case, brought by the Republican-led House of Representatives, are reimbursements to insurance companies to compensate them for reductions that the law requires them to make to customers' out-of-pocket medical payments.