BOSTON (CBS) – The U.S. Supreme Court has upheld most of President Obama’s health care law, ruling Thursday that the individual mandate that requires everyone to buy insurance or face fines is constitutional.

The mandate, which was upheld in a 5-4 vote, will go into effect in 2014.

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Read:  Entire Supreme Court Ruling On Health Care (.pdf)

Chief Justice John Roberts, a conservative, joined the court’s four liberals in deciding the majority opinion.

The ruling means Congress did not exceed its authority when it ordered that all Americans must have health insurance.

In the decision, Roberts wrote that Congress did have the power to pass that mandate because it has the power to tax.

The nation’s highest court also upheld other major provisions of the law, including that insurance must cover pre-existing conditions,  no “lifetime limits” on coverage,  and that children can continue to stay on their parents insurance plans until age 26.

The court did strike down a provision that would expand Medicaid coverage to cover more of the poor.  In the ruling Roberts wrote that was “like a gun to the head of the states.”

To understand the expansion of Medicaid under the Affordable Care Act,  WBZ NewsRadio 1030’s Lana Jones visited Boston University Law School Professor Abby Montcreif, a specialist in health care law:

The Obama administration used Massachusetts as a model for the Affordable Care Act, which the Supreme Court reviewed in three days of oral arguments back in March.

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Read: Reaction From Mass. Lawmakers

Mitt Romney, who’s running against Obama in the November election, signed the Massachusetts plan into law in April 2006 when he was governor.

Romney opposes Obama’s health care reform, and vowed once again Thursday to repeal it if elected, calling it “bad policy” and “bad law.”

“Obamacare raises taxes on the American people by approximately $500 billion,” Romney said in a speech on Capitol Hill, adding that it’s a “job killer” and “puts the federal government between you and your doctor.”

Read: Keller @ Large: How Ruling Affects Obama, Romney

In a nationally televised speech from the White House a short time later, President Obama called the Supreme Court’s decision a victory for “people all over this country.”

Lawrence Tribe, a professor of constitutional law at Harvard University, agreed with the Court’s decision.

“I’m tremendously gratified that the Chief Justice saw it that way and I think he saved the day and perhaps the Court,” he told WBZ NewsRadio 1030.

“What’s most gratifying is the way millions of otherwise uninsured and uninsurable Americans will now learn in real time just how much this landmark and much misunderstood piece of legislation will end up doing to protect people.”

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Tribe taught both President Obama and Chief Justice Roberts at Harvard.