Updated at 5:36 p.m.

The campaign to change the Massachusetts Constitution to create a new surtax on income in excess of $1 million officially kicked off Wednesday, escalating an long-simmering battle that's been brewing since 2015.

The Fair Share Amendment, which is also referred to as the millionaires’ tax, will go before voters as a ballot question this fall. If passed, it would impose an additional tax of 4% on income over the million-dollar mark. The ensuing revenue would be used to fund investments in transportation and education.

Unlike many other states, Massachusetts currently taxes all income levels at the same 5% rate. Previous attempts to amend the constitution to create a graduated income tax have failed, most recently in 1994, when two-thirds of voters rejected the idea.

In a Zoom kickoff event for the millionaires' tax, proponents indicated that they're likely to use the state's experience during the COVID-19 pandemic to make their case for taxing higher incomes at an increased rate.

The Rev. Ann-Marie Illsley, a pastor at Christ Congregational Church in Brockton, praised the efforts of essential workers such as personal care attendants and grocery store employees during the pandemic, and cast passing the proposed amendment as a way to reward their sacrifices.

"In the hardest moments of the pandemic, they stepped up to make sure that our communities had what they needed," Illsley said. "Our essential workers have been putting in their fair share, and they continue to. But these folks and their communities have needs also — needs for better-funded school systems and increased training opportunities, improved infrastructure."

Worcester City Councilor Khrystian King said the amendment would raise approximately $1.3 billion by requiring the state's wealthiest residents to make a relatively small financial sacrifice.

"You're talking about folks that make around $20,000 per week — per week, $20,000," King said. "Those folks are going to have to pay an additional $31 per week.”

An analysis earlier this year by Tufts University's Center for State Policy Analysis also said the amendment would raise about $1.3 billion, and found that it would do so "in a highly progressive way likely to advance racial and economic equity." However, the analysis warned that there could be a "disproportionate effect on state coffers" if just a few of the state's wealthiest residents move out of the commonwealth to avoid a new surtax, and that the shift to hybrid and remote work could lead to more residents relocating than previously anticipated.

The Coalition for a Strong Massachusetts Economy, which opposes the amendment, said people relocating is a likely outcome of the proposed tax hike.

"Proponents of the measure claim that it will raise taxes only on Massachusetts’ highest earners," spokesperson Dan Cence said in a statement, "but in practice, the measure will damage our economy, threaten small business owners, harm retirees, and result in more lost jobs and more people leaving Massachusetts."

Supporters of the proposed amendment had planned to place it before voters in 2018, but the Massachusetts Supreme Judicial Court ruled at the time that the effort, which relied on the state's initiative-petition process, didn't meet specific constitutional requirements.

In this electoral cycle, supporters circumvented a possible repeat challenge by using the referendum process, which is driven by legislative support rather than citizen signatures. In Constitutional Conventions in 2019 and 2021, the Massachusetts House and Senate voted overwhelmingly in favor of advancing the measure to the ballot this year.

Now, opponents are asking the Supreme Judicial Court to amend Attorney General Maura Healey's description of the proposed amendment to convey that the funds raised might not lead to the spending increases advocates promise.

Andrew Farnitano, a spokesperson for Raise Up Massachusetts, which supports the amendment, insisted Wednesday that concern is misplaced.

“Dedicating the funding from the Fair Share Amendment in the text of the constitution is the strongest possible way to ensure that it goes to transportation and public education,” he said. “That is an iron-clad dedication that the funds raised by this amendment must be spent on those two areas.”

An Supreme Judicial Court ruling on the challenge to Healey's summary is expected in the coming weeks.

When Farnitano was asked if the Legislature might diminish spending drawn from other sources if the amendment passes, leading to smaller-than-advertised new investments in education and transportation, he suggested that such maneuvering would be politically risky.

"When you look at the words that they have said and the commitments they have laid out, it's clear that their intention is to spend more on education and transportation," Farnitano said. "And we will hold them to that."

Toward the close of Wednesday's event, campaign manager Jeron Mariani acknowledged that supporters of the proposed amendment have already been campaigning for months.

“We've been out there knocking on doors, open-air canvassing at rallies, making phone calls,” he said.

"This is only going to continue," Mariani added. "And one way that we're continuing it is that this very weekend we're launching seven canvasses — seven different cities, all across the commonwealth.”

Mariani also announced the launch of a new website, fairsharema.com, which he described as a "hub for how to get plugged into the campaign ... to be an active member of this movement."

This story was updated to include a comment from the Coalition for a Strong Massachusetts Economy.