Washington (CNN) Republican Sen. Susan Collins, a key swing vote in the Senate, is asking the Justice Department to reverse its recent support of a total strikedown of the Affordable Care Act, saying the job of eliminating aspects of the health care law should be left to Congress.

"Rather than seeking to have the courts invalidate the ACA, the proper route for the Administration to pursue would be to propose changes to the ACA or to once again seek its repeal. The Administration should not attempt to use the courts to bypass Congress," Collins, who represents Maine, wrote in a letter sent Monday to Attorney General William Barr.

In a dramatic reversal last week, the Justice Department, in a filing with a federal appeals court, sided with the ruling of a federal judge in Texas that invalidated the Obama-era health care law last year.

The Texas ruling came after the Justice Department, under the direction of former Attorney General Jeff Sessions, argued that the community rating rule and the guaranteed issue requirement -- protections for people with pre-existing conditions -- could not be defended but the rest of the law, popularly known as Obamacare, could stand.

The shift in the Justice Department's stance doubles down on stripping away the protections that were a hallmark of the landmark heath reform law.

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