A judge in Texas has ruled that Barack Obama's Affordable Care Act, more commonly known as Obamacare, is unconstitutional in its mandate requiring people to buy health insurance.
The case was brought by a coalition of 20 states that argued that the whole law was invalidated by a change in tax rules last year which eliminated a penalty for not having health insurance.
The judgment has been hailed as a victory by U.S. President Donald Trump who has always been fiercely critical of Obamacare.
The states challenging the law were led by Texas Attorney General Ken Paxton and Wisconsin Attorney General Brad Schimel, both Republicans.
The 2010 law was the signature domestic policy achievement of Trump's Democratic predecessor Barack Obama.
Since its inception, Republicans have repeatedly tried and failed to repeal it.
It's thought the case could go all the way to the U.S Supreme Court.