A demonstrator holds a sign in support of President Barack Obama's health-care law, Obamacare, in front of the U.S. Supreme Court in Washington, on Wednesday, March 4, 2015.

Obamacare will once again face a test at the nation's highest court.

The Supreme Court said Monday that it will hear an appeal brought by Democratic-led states seeking to affirm the constitutionality of the Affordable Care Act, President Barack Obama's signature health-care legislation.

The states, led by California, have urged the justices to reverse a lower court ruling that found the law's individual mandate provision unconstitutional.

The appeal comes after the federal appeals court based in New Orleans ruled late last year that the individual mandate provision of the Affordable Care Act was unlawful. The court sent the rest of the law back to a lower court to determine if it could still stand.

The states urged the justices to take the case and resolve it this term, ahead of the 2020 presidential election. The top court did not indicate when it will hear the case, but it will likely do so in its term beginning in October. A decision would be expected by the end of June 2021, after the next presidential term has begun.

The case is the latest challenge to the law, more commonly known as Obamacare, which has twice before withstood challenges at the Supreme Court.

Obamacare has been the target of Republican attacks in the courts since it was first passed nearly 10 years ago. It has so far withstood scrutiny from the justices. The current lawsuit against it is based on a technical reading of Chief Justice John Roberts' reason for upholding the law in 2012.

Roberts, writing for the court at the time, upheld the individual mandate provision because he said it fell within Congress' power to tax.

But, in 2017, Congress lowered the penalty for not having insurance to $0 as part of Trump's tax reform push. Republican states, led by Texas and backed by the Trump administration's Department of Justice, have contended that the effective elimination of the penalty meant the individual mandate could no longer stand as a tax.

The Trump administration has argued in court that the entire law should be eliminated.

Judge Reed O'Connor of the Northern District of Texas ruled in favor of Obamacare's challengers in December 2018. O'Connor also held that the rest of the Affordable Care Act was not "severable" from the individual mandate, essentially scrapping the whole law.

On review, the 5th U.S. Circuit Court of Appeals agreed with O'Connor that the individual mandate was unconstitutional, but urged him to review the law with a "finer-toothed comb" to determine "which provisions of the ACA Congress intended to be inseverable from the individual mandate."

Seeking to avoid the uncertainty that an ongoing battle in the lower courts would entail, the Democratic states and the House of Representatives filed separate petitions urging the Supreme Court to settle the matter quickly. The court denied the request to expedite arguments in January.

Roberts and the four liberals who voted to uphold the law remain on the bench.