A three-judge panel unanimously said the law was ambiguous, and that it would defer to the IRS's determination that subsidies could go to individuals who purchased health insurance on both federal and state-run exchanges.

The U.S. Court of Appeals for the Fourth Circuit upheld a federal regulations that implemented subsidies that are vital to President Barack Obama 's healthcare overhaul, in direct conflict with another ruling on the issue handed down earlier on Tuesday.

A separate panel from a federal appeals court in Washington on Tuesday morning said the IRS could not offer premium tax credits to people who purchase insurance through the federal insurance marketplace that serves most of the 8 million consumers who have signed up for private coverage for 2014.

Analysts estimate that as many as 5 million people could be affected if subsidies disappear from the federal marketplace, which serves 36 states through the website HealthCare.gov.

The subsidies are available to people with annual incomes of up to 400 percent of the federal poverty level, or $94,200 for a family of four.

—By Reuters