The ruling in Virginia strikes the most serious legal blow yet to the Obama-backed law requiring Americans to get health insurance.

A federal judge in Virginia on Monday rejected part of the new healthcare law, becoming the first court to rule that Congress had placed an unconstitutional requirement on Americans to get health insurance.

The much-anticipated decision, which the Obama administration is expected to appeal, will not stop implementation of the sweeping overhaul that the president signed in March.

The new mandate is not set to go into effect until 2014, when Americans will also gain guarantees that they will be able to get health benefits even if they are sick.

On Monday, U.S. District Judge Henry Hudson denied a request from Virginia Atty. Gen. Ken Cuccinelli, the lead plaintiff, to stop implementation of the law while higher courts consider the case.