The U.S. Supreme Court, for the second time in three years, has affirmed the legality of key provisions of the 2010 Patient Protection and Affordable Care Act,  a measure that is viewed as one of President Obama's central legislative achievements.

In a 6-3 opinion issued on June 25, the court said that federal tax credits that enable individuals who cannot otherwise afford health insurance to purchase coverage are permissible under the Affordable Care Act and are in line with what Congress intended when it wrote the law.

The ruling is a clear victory for the administration, and for President Obama. But contractor groups say that they will continue to push for more construction-friendly changes to the law or outright repeal.

Since the measure was enacted, the Republican-controlled House has voted to alter or repeal the law about 50 times. But few changes have been enacted.

The constitutionality of the law’s “individual mandate” was also the subject of an unsuccessful legal challenge before the Supreme Court in 2012.

Writing for the court's majority in the new case, King v. Burwell, Chief Justice John G. Roberts Jr., said: “Congress passed the Affordable Care Act to improve health insurance markets, not to destroy them. If at all possible, we must interpret the act in a way that is consistent with the former, and avoids the latter.”

Reaction to the decision was swift and deeply divided. GOP leaders, including House Speaker John Boehner (R-Ohio) and Senate Majority Leader Mitch McConnell (R-Ky.), vowed to continue to work to repeal “Obamacare.”

The law’s supporters, including Obama and leading congressional Democrats, praised the decision. Shortly after the opinion was released, the president told reporters, “After 50 votes in Congress to weaken or repeal this law…the Affordable Care Act is here to stay.”

He added that if the legal challenge to the law had succeeded “millions of Americans would have thousands of dollars of tax credits taken from them. For many, insurance would become unaffordable again.”

Construction contractor groups said that the law has caused premiums to rise for a large number of small-business owners and added that they will continue to press for Congress to change or repeal the law.

“It still remains a top legislative priority for us to see Obamacare repealed and replaced with something that addresses the needs of contractors,” said Brian Turmail, Associated General Contractors of America senior director of public affairs.

Jeff Leieritz, a spokesman for the Associated Builders and Contractors, said, “We are disappointed in the ruling” and added that marshaling congressional support for ACA repeal is one of ABC's legislative priorities.

One of the most problematic provisions for contractors, Turmail notes, is the requirement that multi-state employers enroll employees working in different states in different exchanges or plans.

In the meantime, AGC is helping its members to comply with the ACA, and this year began offering an insurance program in which its member firms can participate, Turmail said.

John Grau, the National Electrical Contractors Association's CEO, said in a statement that the ruling creates an opportunity to fix other provisions that NECA finds problematic.

Grau said: "Congress should enact meaningful reforms, including repeal of the 40% excise tax on employer-sponsored health care. This tax punishes NECA contractors for providing employees with quality health coverage. The vast majority of our plans will be hit with this tax."

Grau is referring to a provision that taxes high-benefit "Cadillac" health insurance plans.

At the heart of the case was ACA language that said the tax subsidies were available only to those who enrolled in an exchange “established by the State.”

Roberts wrote that the phrase, taken in isolation, is “ambiguous.” But in the broader context of what Congress intended in writing the law, it could be interpreted to suggest that the "state" also includes federal subsidies.

He said: “Without the tax credit, the coverage requirement would apply to fewer individuals.…It is implausible that Congress meant the act to operate in this manner.”

The case arose from a complaint from four people in Virginia who did not want to enroll in a health plan, and did not want to receive a federal tax subsidy to do so.

A lower court dismissed the suit, saying that the language of the law was clear that the tax credits would be available in a federal exchange.

A federal appeals court said that the language was “ambiguous” and remanded the case to be resolved by the Internal Revenue Service.

In a dissenting opinion, Associate Justice Antonin Scalia, joined by Justices Samuel Alito and Clarence Thomas, called the majority’s interpretation “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?'"