In a case successfully argued by Northeastern University law professor Wendy Parmet, the Massachusetts Supreme Judicial Court ruled on Thursday that the state could not exclude legal immigrants from subsidized health insurance.

“We are very pleased for our clients and for the people who have gone without health care for a long time,” said Parmet, Matthews Distinguished University Professor of Law, who argued the case on behalf of the immigrants who were cut from Commonwealth Care in 2009 in a state budget-cutting move. “We are very hopeful now that their health insurance coverage will be restored very quickly.”

The litigation was brought to court by Health Law Advocates, a public-interest law firm for which Parmet once served as board president.

The ruling reverses 2009 legislation that excluded some 29,000 legal immigrants who had lived in the United States for less than five years from the Commonwealth Care program, which has helped cover insurance premiums for low-income Massachusetts residents since 2006. After funding for the program was slashed two years ago, many immigrants were moved to a cheaper state plan that offers fewer health-care providers and requires participants to pay higher fees for prescriptions and doctor’s visits.

Following that legislation, Health Law Advocates lobbied the legislature to repeal the law, hoping to avoid litigation.

“But there wasn’t going to be a remedy short of going to court,” Parmet said, describing the group’s decision to begin legal proceedings.

In the court’s ruling, Justice Robert Crody wrote, “We recognize that our decision will impose a significant financial burden on the Commonwealth,” but noted that costs couldn’t justify a violation of legal immigrants’ equal protection under the law.

Parmet expects the court will soon issue an order to the Legislature to repeal its law and restore equal access to subsidized health care to legal immigrants. “The court ruled that the state Legislature cannot solve its fiscal problems on the backs of legal immigrants,” Parmet said. “It’s a very clear, decisive and unanimous opinion that sends a clear message to the Legislature.”

Co-op students, faculty members and recent alumni helped Parmet research the pro bono case. The case was “a real Northeastern effort,” she said.