US District Judge Reed O'Connor in Fort Worth agreed with a coalition of Republican states led by Texas that he had to eviscerate the Affordable Care Act, the signature health-care overhaul by President Obama, after Congress previous year zeroed out a key provision - the tax penalty for not complying with the requirement to buy insurance.
Supporters of the law immediately said they would appeal.
"The court ... declares the Individual Mandate UNCONSTITUTIONAL", Reed judgment concludes.
The decision is a huge swipe at the 2010 health law and sets the stage for a bigger fight in appeals courts.
Lawyers for the Department of Justice had suggested that O'Connor should not rule until after the open enrollment period for the 2019 plan year ends on December 15 in order to avoid disrupting the markets.
"When House Democrats take the gavel, the House of Representatives will move swiftly to formally intervene in the appeals process to uphold the life-saving protections for people with pre-existing conditions and reject Republicans' effort to destroy the Affordable Care Act", Mrs. Pelosi said.
A federal Fort Worth judge filed a decision in a national Obamacare ruling on Friday, casting doubt on coverage for millions of Americans.
The decision was a break with a long-standing executive branch practice of defending existing statutes in court. "Congress severed that thin thread with the tax act of 2017, and all of Obamacare must fall".
White House press secretary Sarah Huckabee Sanders said: "We expect this ruling will be appealed to the Supreme Court". Justice officials contended that, once the insurance mandate's penalty is gone next month, that will invalidate the ACA's consumer protections, such as its ban on charging more or refusing to cover people with preexisting medical conditions. President Donald Trump tweeted that Congress should pass a new law. Meanwhile, a number of states are expected to move forward with Medicaid expansion after Democratic victories in the midterm elections.
Judge O'Connor ruled that, therefore, the mandate without a tax penalty attached was unconstitutional, and so too the rest of the law. A group of Republican state attorneys general argued in their lawsuit that the repeal of the tax penalty gutted the argument for ACA legality. In Maine, outgoing Gov. Paul LePage, R, joined the lawsuit, but the state attorney general's office told the court last month that the governor did not have power to do so on his own.