For years, most states protected homeowners who were delinquent on their local property taxes from losing all the equity they had in their homes in tax foreclosure cases.

But Massachusetts and a handful of other states didn’t, allowing municipalities to keep millions of dollars in equity in such cases, far exceeding what property owners actually owed in taxes, penalties, and interest.

But a US Supreme Court ruling last week deemed the practice, which critics call “home equity theft,’’ unconstitutional and casts doubt on what is done in Massachusetts.

The Supreme Court, in a rare unanimous ruling, said it was unconstitutional for a local government in Minnesota to keep all of the money it got when it sold a condo seized from the owner due to unpaid taxes.

The owner owed $15,000 in taxes, penalties, and interest, but the condo sold for $40,000. Under Minnesota law, the local government was legally permitted to keep all $40,000, including the $25,000 the owner had in equity.

But the Supreme Court ruled the local government violated the Fifth Amendment by taking the owner’s $25,000 in equity. The Fifth Amendment, among other things, prohibits the government from taking private property without compensation.

The ruling has potentially far-reaching implications in Massachusetts for municipalities and the private companies that sometimes purchase their tax liens. In recent years, they have seized equity in hundreds of tax foreclosure cases.

The Supreme Court decision struck down the Minnesota law on tax foreclosures, but the high court didn’t rule directly on the Massachusetts law, which is different from Minnesota’s in that it provides for judicial oversight of the foreclosure process, including some control over the disposition of equity.

Still, the Massachusetts law as now written is likely to be declared unconstitutional when and if it gets challenged by a homeowner in court, according to lawyers familiar with the ruling.

“In light of [the ruling] I believe the Massachusetts practice of retaining surplus proceeds on tax lien foreclosures … is unconstitutional and always has been unconstitutional,’’ said Edmund Allcock, a lawyer who has previously challenged the Massachusetts tax foreclosure law.

In the absence of a case that tests the constitutionality of the Massachusetts law, however, the state Legislature should pass a law explicitly protecting homeowners’ equity, Allcock said.

“I don’t believe there is any way around [the Supreme Court ruling],’’ he said. “Which is good. Nobody should get more than what they are entitled to in any foreclosure. But there’s nothing wrong with mandating it legislatively. It’s the right thing to do.’’

There are at least two bills pending in the Legislature that would abolish the taking of equity by municipalities and private companies. State Representative Tommy Vitolo, a cosponsor of one of the bills, said the Supreme Court ruling may energize those who support the proposed legislation.

“It’s important to remove from existing state law something that’s unethical, inappropriate, and, now, according to the Supreme Court, unconstitutional,’’ Vitolo said in an interview. “We want to clean it up.’’

In a statement released by Vitolo and two cosponsors of the measure, Representative Jeffrey N. Roy, and Senator Jo Comerford, the legislators said: “We remain committed to ridding Massachusetts law of this unfair, and now unconstitutional, practice.’’

Senator Mark Montigny, sponsor of a similar bill, called for an end to “this predatory practice.’’

The homeowner in the Minnesota case was represented pro bono by Pacific Legal Foundation, a national public interest law firm that has said its goal is complete elimination of what it calls “home equity theft.’’

“This ruling ends ‘equity theft’ and protects ordinary people from government overreach,’’ said Joshua Polk, a Pacific Legal Foundation lawyer who was involved in the case.

“It means the government can rightfully take what it is owed in taxes, but not one dollar more,’’ he said.

For the sake of clarity, Polk encouraged the Massachusetts Legislature “to change its law to be consistent with this ruling.’’ Pacific Legal Foundation is reaching out to all states that allow local governments to take equity in tax foreclosure cases to help them draft bills that would end the practice.

Geoff Beckwith, executive director of the Massachusetts Municipal Association, said the Legislature should create a special commission to consider how the Supreme Court ruling may affect municipal tax collection. Many municipalities already consider the tax-taking process to be too slow and laborious, sometimes depriving them of needed tax revenue due to default for years, he said.

He said a commission may come up with ideas for assisting municipalities in tax collections without violating constitutional rights.

Many cities and towns in Massachusetts in recent years have pursued equity takings in tax foreclosure cases or sold tax liens to private companies.

In a recent study of 31 municipalities in Massachusetts, representing about one-third of the state’s population, Pacific Legal Foundation identified 308 tax foreclosures between 2014 and 2020 in which a municipality or a private company took a property owner’s entire equity.

In 254 of those cases, the municipality received $60 million above what the homeowners owed in property tax debt, according to the study.

And in 154 cases, a private company received $37 million above what the homeowners owed in property tax debt, the study found.

On average, Massachusetts homeowners subjected to tax foreclosure lost 87 percent of their home equity — almost $260,000 per home, the study found.

Daniel C. Hill, a lawyer for Tallage LLC, one of the most active companies in purchasing municipal tax liens, said he believes the Massachusetts law will survive a constitutional challenge because of its judicial involvement and other protections for homeowners, although some legislative tinkering may be in order.

“I could also envision some imminent legislative changes that would expand protections and thus insulate the statute from [legal] attack,’’ he said.

Last year, the Globe reported on the case of Deborah Foss, who lost more than $200,000 in equity in her New Bedford home. After the column appeared, she won $85,000 in a legal settlement with Tallage.

In 2021, the Globe featured the plight of two brothers, Mark and Neil Mucciaccio, who were behind on the taxes on their Easton home. At the time, Tallage appeared well on its way to legally gaining title to their home — and keeping all the equity.

After the column appeared, the brothers managed to slow down the legal process long enough for a family member to step up with a loan. That saved their house and $255,000 in potential lost equity. They continue to live there now with their families.

“I’m so pleased the Supreme Court voted out this injustice,’’ Mark Mucciaccio said of the ruling in the Minnesota case. “I just hope it means this will never happen to anyone else.’’

Got a problem? Send your consumer issue to sean.murphy@globe.com. Follow him on Twitter @spmurphyboston.