In a 6-3 decision, the Supreme Court of the Unites States has upheld a crucial element of the Affordable Care Act (ACA), stating that those who buy healthcare through the federal marketplace should receive taxpayer subsidies.

The ruling, which preserves health insurance for millions of Americans, marks a second major victory for President Barack Obama in preserving what has become one of the most significant achievements of his presidency, and a favorite target of the Republican political opposition.

"The ACA is here to stay," Obama said in remarks delivered after the court's ruling. "Today is a victory for hard-working Americans all across this country."

The plaintiffs in King v. Burwell had argued that Congress did not authorize the federal subsidies and tax credits central to the healthcare law, since the text of the law is vague about their funding source.

The ACA relies on a system of state-level and federal exchanges where Americans can buy healthcare with the help of subsides and tax credits. In 34 states that declined to set up their own exchanges, healthcare seekers can purchase plans on exchanges established by the federal government.

The suit sought to rollback the tax subsidies behind these federal exchanges because the wording of the initial ACA referred to funding for exchanges "established by the State."

'Congress passed the Affordable Care Act to improve health insurance markets, not to destroy them.'

The Obama administration had argued that opponents of the ACA were misrepresenting the legislature's intent and quibbling over the definition of the word "state." In his majority opinion, Chief Justice John Roberts agreed.

"The combination of no tax credits and an ineffective coverage requirement could well push a State's individual insurance market into a death spiral," he wrote. "It is implausible that Congress meant the Act to operate in this manner."

Roberts argued that upholding the law aligned with the legislature's initial intent.

"Congress passed the Affordable Care Act to improve health insurance markets, not to destroy them," he said. "If at all possible, we must interpret the Act in a way that is consistent with the former, and avoids the latter."

Roberts was joined by Justices Anthony Kennedy, Ruth Bader Ginsburg, Stephen Breyer, Elena Kagan, and Sonia Sotamayor in his decision.

'We should start calling the law SCOTUScare.'

In a strongly worded dissent, Justice Scalia suggested that the Supreme Court was overstepping its bound and writing its own laws.

"Normal rules of interpretation seem always to yield to the overriding principle of the present Court: The Affordable Care Act must be saved," he wrote."We should start calling the law SCOTUScare."

"Today's interpretation is not merely unnatural; it is unheard of," Scalia added. "Who would ever have dreamt that 'Exchange established by the State' means 'Exchange established by the State or the Federal Government'?

Justices Samuel Alito and Clarence Thomas joined Scalia in his dissent.

Politicians were quick to respond to the landmark decision on social media Thursday morning.

Yes! SCOTUS affirms what we know is true in our hearts & under the law: Health insurance should be affordable & available to all. -H — Hillary Clinton (@HillaryClinton)June 25, 2015

Despite the Court's decision, ObamaCare is still a bad law that is having a negative impact on our country and on millions of Americans. — Marco Rubio (@marcorubio)June 25, 2015

Obamacare is the law of the nation. Republicans should stop wasting the time of the American people by trying to repeal it. Let's move on. — Senator Harry Reid (@SenatorReid)June 25, 2015