Freedom from income taxes is a New Hampshire delight: The Granite State is one of nine that don’t tax ordinary income. Of course, that benefit doesn’t apply to New Hampshire residents who commute to work across the Massachusetts border. Income earned inside Massachusetts by an out-of-state resident is subject to Massachusetts taxes.

What about a New Hampshire resident who used to commute to Massachusetts?

A no-brainer, surely. If you don’t live in Massachusetts, and you no longer work in Massachusetts, then Massachusetts has no right to tax your earnings. What could be more self-evident?

Until last spring, that was the law. The Massachusetts Department of Revenue itself said so: “Compensation for services rendered by a non-resident wholly outside Massachusetts, even though payment may be made from an office or place of business in Massachusetts,” the department affirmed in a 1984 ruling, “is not subject to the individual income tax.” And if a New Hampshire resident employed by a Massachusetts company divided his hours between Massachusetts and New Hampshire? In that case, “only that portion of his salary attributable to his work in Massachusetts will be taxed.”

Then came the pandemic. Massachusetts declared an emergency and ordered non-essential workplaces to close. Many of the 84,000 New Hampshire residents who had been commuting to jobs in the Bay State switched to working from home. Under the rule that had been in place for decades, Massachusetts could no longer tax their income.

So it invented a new rule.

In April, the Department of Revenue published an “emergency regulation” declaring that any income earned by a nonresident who used to work in Massachusetts but was now telecommuting from out of state “will continue to be treated as Massachusetts source income subject to personal income tax.” For the first time ever, Massachusetts was claiming the authority to tax income earned by persons who neither lived nor worked in Massachusetts.

Not surprisingly, New Hampshire strenuously objected to its neighbor’s unprecedented tax grab. When Massachusetts refused to reconsider, New Hampshire turned to the Supreme Court, which adjudicates lawsuits between states. The justices are expected to decide this month whether to take the case.

Massachusetts, naturally, wants the justices to give New Hampshire the brush-off. A brief filed by Attorney General Maura Healey disparages New Hampshire’s complaint as lacking “seriousness and dignity” and insists that Massachusetts “is not injuring New Hampshire itself” by withholding millions of dollars in taxes from the paychecks of New Hampshire residents. If any of those residents object to being taxed by Massachusetts, Healey’s brief suggests, they can always file for an abatement. If that doesn’t work, they can always appeal to the Appellate Tax Board. Why should the Supreme Court concern itself with what amounts, at most, to the personal tax gripes of New Hampshire telecommuters?

But Massachusetts has indeed injured New Hampshire itself. It has launched what amounts to an attack on a fundamental aspect of New Hampshire’s sovereign identity — its principled refusal to tax the income earned in New Hampshire by New Hampshire residents. It was one thing for Massachusetts to withhold taxes from New Hampshire residents for income earned within the borders of Massachusetts. But with its new tax rule, Massachusetts is reaching over the border to extract taxes, thereby undermining a core New Hampshire policy.

“Through its unprecedented action,” the New Hampshire brief argues, “Massachusetts has unilaterally imposed an income tax within New Hampshire that New Hampshire, in its sovereign discretion, has deliberately chosen not to impose.”

New Hampshire isn’t fighting alone. Fourteen other states have filed briefs urging the Supreme Court to take up its complaint. They urge the justices to reassert and reinvigorate a basic principle of the Constitution’s federal system: that the power of states to tax nonresidents’ income does not extend past their own borders.

To be fair, Massachusetts isn’t the first state to violate the principle. A few states, including New York and Pennsylvania, have for years been taxing nonresidents for income they earn working at home. Resentment by other states has been heating up for years. Now the pandemic, by transforming tens of millions of employees into work-from-home telecommuters overnight, may have pushed the issue past the boiling point.

States with no income tax, like New Hampshire, aren’t the only ones affected when their work-from-home residents are taxed by another state. So are states that do tax income, because they commonly provide a credit to residents for taxes paid to other states. That protects their own citizens from double taxation — but it also means the loss of billions of dollars that would otherwise be available to fund public services. In one of the briefs supporting New Hampshire’s litigation, New Jersey, Connecticut, Hawaii, and Iowa call this “the Hobson’s Choice to which they are put: doubly tax residents’ income or suffer fiscal consequences.”

According to the National Taxpayers Union, at least 2.1 million Americans who previously crossed state lines for work are now working from home because of COVID-19 restrictions. When the pandemic ends, remote work is expected to remain far more common than it used to be. The unfairness of what Massachusetts began doing last spring, and of what a few other states have been doing for much longer, will grow more galling. Only the Supreme Court has the power to shut down such overreaching. Now, thanks to New Hampshire, it has the opportunity.

(Jeff Jacoby is a columnist for The Boston Globe).