In a monumental ruling, the United States Supreme Court on Thursday upheld the Patient Protection and Affordable Care Act of 2010, including the controversial mandate that requires individuals to purchase health insurance beginning in 2014.

In a 5-4 vote, the court contended that the law is constitutional and that the mandate is a tax and not a penalty, as originally described by supporters. 

Hundreds of people gathered on the steps of the Supreme Court building in downtown Washington, D.C., before the ruling came out just after 10 a.m., holding signs with slogans like “Medicare for all” and chanting refrains like “strike it down!"

Chief Justice John Roberts, a conservative appointed by President George W. Bush, went against party lines to tip the decision in favor of the Obama administration with liberal Justices Sonia Sotomayor, Stephen Breyer, Ruth Bader Ginsburg and Elena Kagan voting with the majority that the Affordable Care Act is constitutional.

The court reasoned that the hotly debated individual mandate provision is constitutional under Congress’ power to tax, also known as regulation of commerce. Since the mandate survived, the Court did not need to weigh in on whether other parts of the law are constitutional, except for the Medicaid expansion. 

While the court upheld the individual mandate, the future of the health reform law’s planned Medicaid expansion is a bit murky. The court sustained the Medicaid expansion but said if a state chooses not to participate in the expansion to the newly eligible population, Congress may only withhold funding from the new category of individuals that would qualify for Medicaid under the parameters of the Affordable Care Act. If states accept expansion funds, they must do so under the condition that they obey new rules. Essentially, this means the Medicaid expansion is optional for states.

Starting in 2014, the health reform law would make millions of additional Americans eligible for Medicaid benefits by raising the eligible income level to 133 percent of the federal poverty level to qualify. Initially, the federal government will pay for this expansion, but after a period of time federal funding will drop off and states will have to pick up the tab.

Opponents of the Medicaid expansion have argued that the provision places an undue burden on states while diminishing their autonomy. But states that do not expand Medicaid may have to deal with a continued influx of low-income, uninsured patients into emergency departments, further driving up healthcare costs in the form of uncompensated care for hospitals.

Overall, healthcare associations and patient advocacy organizations lauded Thursday’s Supreme Court decision, stressing the benefits of expanded insurance coverage and improved access to preventive health services.

“We are pleased by the Court's decision today to uphold the Affordable Care Act's individual mandate, which will broadly expand healthcare coverage. We also are pleased that the decision retains other positive elements of the ACA, including initiatives to promote innovation, preventive care, and community-based collaborations,” the National Association of Public Hospitals and Health Systems said in a statement.

However, the organization said it is concerned about the ruling’s potential to limit Medicaid expansion since 26 states participated in the federal lawsuit challenging the constitutionality of the Affordable Care Act.

The National Nurses Association also expressed support for the ruling, pointing out that the Court decision will help improve care coordination among patients – a major shortcoming in the U.S. healthcare system – and ultimately, drive down costs.

“Instead of getting sicker and developing serious and costly complications because they can’t afford to manage their health conditions, people will get the care they need to recognize problems earlier or avoid them altogether,” ANA President Karen A. Daley said in a statement.

Healthcare professionals can expect the law’s other reforms, many already underway, to continue. These include the Hospital Value-Based Purchasing program, payment penalties for health care-associated conditions and avoidable readmissions, and testing of new payment and delivery models like bundled payments and shared savings.

Today’s ruling also means that a provision allowing young adults up to age 26 to stay on their parents’ health insurance – a piece of the legislation popular with both Democrats and Republicans – will remain in effect.