The future of health-care coverage for millions of Americans was thrown into uncertainty Friday when a federal judge in Texas struck down Obamacare.

U.S. District Judge Reed O'Connor ruled the Affordable Care Act is unconstitutional because it no longer includes a tax penalty for those who refuse to comply with the requirement to buy insurance, according to published reports. That provision was stripped out of the law last year by Congress.

O'Connor sided with the claims of 20 Republican states and the Trump administration that had filed suit in a bid to scuttle the ACA, claiming it was no longer constitutional without the tax penalty.

The immediate impact of the ruling is not clear, though the White House indicated the ruling would be on hold pending appeals that are likely to reach the Supreme Court.

Still, President Donald Trump lauded the decision in a tweet:

If upheld, the decision could eliminate health coverage for millions of people with pre-existing conditions.

Saturday marks the deadline for signing up for Obamacare for next year. As many as 20 million people are currently covered by the health law.