The House, which as of Thursday is controlled by Democrats and led by Speaker Nancy Pelosi of California, asked a federal judge in Texas to allow it to intervene in the case.
The filing moves the legal defense of the ACA to the Fifth Circuit Court of Appeals, where the AG's will appeal the lower court's ruling that the ACA is unconstitutional. O'Connor stayed his ruling pending appeal.
House Democrats used their new majority on Thursday to squeeze Republicans on health care, taking the first step to intervene in a court case in which a Texas judge has ruled the Affordable Care Act unconstitutional. A vote on the largely symbolic effort is expected soon.
The House filing said that its "interest in this action.is not adequately represented by the existing parties".
133 million Americans with preexisting health conditions.
California is once again defending the Affordable Care Act, leading a coalition of Democratic states against a small army of Republican lawmakers seeking to undo the Obama administration's signature healthcare law.
Becerra reminded reporters on the call that it was Republican state officials who started the lawsuit, which seeks to dismantle the law and its consumer protections entirely. But the fact that Republicans remain in control of the Senate may thwart such any such effort, and it nearly certainly would be vetoed by President Trump if it did clear Congress.
California's coalition will continue to defend the law against this unfortunate decision that could wreak havoc on the entire American healthcare system and risk lives in every state. Thus, O'Connor's ruling was just judicial activism and political hackery. Those provisions include prohibitions on insurers charging higher premiums or denying coverage for people with pre-existing health conditions.
Oregonians who enrolled in coverage during open enrollment must pay their premium when they receive their January bill in order to make the coverage effective.
The claim made by the states opposing the ACA was that the government requirement for people to have health insurance is unconstitutional in nature as the mandate was coupled with a tax penalty for those who did not have insurance coverage.
At a White House Cabinet meeting Thursday, President Donald Trump declared, "That case from Texas should win in the Supreme Court".
That move will be followed by a vote next week created to force GOP lawmakers into a political corner: agree to defend a law many members have spent years reviling or appear to oppose popular ACA protections for millions of Americans with preexisting medical conditions that many have pledged to uphold.
While that argument is widely disputed, even by long-standing critics of Obamacare, O'Connor endorsed it with his ruling.
The Democratic states have stepped up to defend the law because the Trump administration has declined to do so.