A federal judge’s recent ruling that the entire Affordable Care Act is unconstitutional could threaten the immediate coverage of 1.2 million young adults. Judge Roger Vinson of the Northern District of Florida ruled the responsibility provision, which mandates that all Americans have to buy healthcare insurance, is unconstitutional, making the whole law void.

If this ruling is upheld it could threaten the coverage of more than one million young adults who are able to stay on their parent’s plan up to age 26. While the whole insurance mandate will not take effect until 2014, some new regulations have already been implemented. These include requirements that insurers cover children with pre-existing conditions and the mandatory inclusion of young adults on their parents’ plans.

The much-debated health law has seen legal challenges from plaintiffs including governors and attorneys general from twenty-six states. The Florida judge’s ruling has created an equal division in federal court decisions on the law—two Democrat-appointed judges have upheld it and a Virginian Republican appointed judge also ruled against it, calling it unconstitutional.

The House of Representatives voted to repeal the law in January, but Senate majority leader Harry Reid vowed to prevent a vote in the Senate. The White House announced that it would appeal yesterday’s ruling.

A health care advocacy group ‘Young Invincibles’—taken from the name insurance companies use to describe the demographic of 18-to-29-year-olds—plans to file a brief in the court of appeals.

“Young Americans need the protections and new options for coverage provided by the Affordable Care Act,” said Aaron Smith, executive director of Young Invincibles. “Judge Vinson’s ruling has taken judicial activism to the extreme, and puts the health and well-being of all Americans at risk.”