Proponents of a proposed surtax on income over $1 million — commonly referred to as the Fair Share Amendment or millionaires' tax — won a major victory Wednesday when the Massachusetts Supreme Judicial Court upheld the language that will be used to describe the ballot question for voters this November.

Supporters say the measure will fund increased state investments in education and transportation via a new 4% surtax on income in excess of $1 million, which will effectively create a graduated income tax in Massachusetts. The Massachusetts Constitution currently prohibits such a tax, and six previous attempts to amend the constitution to create one have failed.

Critics say investment in education and transportation won't necessarily increase if the measure passes, because the Legislature could simply use those new tax dollars to maintain existing spending levels while shifting prior funding to other areas. They had argued that a summary prepared by Attorney General Maura Healey for the November ballot and prior distribution to voters, and even briefer one-sentence synopses Healey and Secretary of State Bill Galvin wrote for the ballot, failed to adequately convey this scenario and should be revised.

In an opinion issued Wednesday morning, the SJC rejected that argument, saying Healey's summary "describe[s] the amendment itself ... fairly" and that the briefer one-sentence synopses prepared by Healey and Galvin are neither false nor misleading.

The Fiscal Alliance Foundation, which had filed an amicus brief in support of revision, decried the ruling in a statement, stating that Healey, Galvin, and the SJC "have all dropped the ball" and that the language used to describe the effects of the ballot question for voters "is extremely leading."

In contrast, the Fair Share for Massachusetts campaign applauded the ruling in a statement, saying the existing language "accurately describes what the Fair Share Amendment will do."

Earlier this year, an analysis from Tufts University's Center for State Policy Analysis found that the proposed amendment would raise $1.3 billion and was "likely to advance racial and economic equity." However, the center also warned that some of the state's wealthier residents could relocate to avoid the new tax, and that state tax revenues could suffer as a result.

This story is developing.