REP. JAY KAUFMAN has been a reliable member of the House Democratic caucus’s progressive wing for more than 20 years.

In the 1990s, he was part of a small band of liberal lawmakers who clashed regularly with then-Speaker Tom Finneran — and found themselves relegated to legislative Siberia as a result.

But Kaufman found his way back in from the cold, working his way into the good graces of Finneran’s successor, Sal DiMasi, who tapped him to co-chair the Joint Committee on Revenue, a post that he has continued to hold for the last seven years under Speaker Robert DeLeo.

Unlike many state lawmakers, Kaufman doesn’t have an aversion to talk of new taxes. He scoffs at the “Taxachusetts” moniker as outdated and has no qualms about opposing popular measures like the annual sales tax holiday, which he worries drains valuable revenue from state coffers.

Rep. Jay Kaufman of Lexington
Rep. Jay Kaufman of Lexington

Despite what may seem like the ideal perch for advancing his views, at the helm of the Revenue Committee, Kaufman has not been able to mount much of a drive for new taxes under the fiscally moderate DeLeo, who tends to tamp down any talk of new levies on taxpayers.

But for the Lexington liberal and fellow House members who veer left on fiscal policy, their revenue ship may have come in. If the Legislature won’t make a big move to raise taxes, maybe the voters will.

That’s the hope of Raise Up Massachusetts, the coalition of unions and other activists pushing for a constitutional amendment that would raise the state income tax on those earning more than $1 million per year. The so-called “millionaire’s tax” is aimed at bringing more money into state coffers to fund services, while also blunting, at least a little, rising income inequality that has seen high earners in the US race ahead as real income has stagnated for most everyone else.

Kaufman has emerged as a point man in the Legislature for the Raise Up Massachusetts ballot question campaign.

“We’ve gotten kind of used to thinking of us and them,” says Kaufman. “There are plenty of good reasons to think that it is as much in the interest of the wealthiest among us not to have this wealth and income divide.”

In 2014, Kaufman co-chaired with Sen. Michael Rodrigues, his revenue committee cochairman, a Tax Fairness Commission that explored ideas for bringing greater equity to the tax code. Its lead recommendation was a constitutional amendment to have upper earners pay higher income tax rates.

The measure now being pushed would tack 4 percentage points onto the 5.15 percent income tax rate for those in the million-dollar-plus bracket. Supporters estimate it would affect about 14,000 taxpayers and generate an additional $1.3 to $1.4 billion a year in tax revenue.

Associated Industries of Massachusetts, a major voice of business in the state, says the proposed constitutional amendment would be a major blow to businesses such as subchapter S corporations that are taxed at the individual rate. AIM also says the measure shouldn’t have been allowed on the ballot because it usurps the Legislature’s power by effectively appropriating money for education and transportation.

An initiative petition to change the state constitution faces a longer road to the ballot than one designed simply to enact or change a state law. In addition to gathering signatures from about 65,000 voters, advocates must win the support of 50 of the 200 representatives and senators in two separate sessions of the Legislature in order to get the measure onto the ballot. That means the earliest it could go before voters is 2018.

Though it’s unclear how much support the measure will receive from House leaders, liberal supporters of the initiative say they are merely allowing voters to be heard on the issue by advancing the measure to the ballot.

Kaufman sees a “growing will’ in the House to let voters decide, so he is glad-handing as many of his 160 House colleagues as he can. “We are not going to tell the public how to do this,” he says. “The public is going to tell us how we are going to do this.”

Kaufman “really understands the benefit of having fair revenue, meaning fair and adequate revenue,” says Harris Gruman, executive director of the SEIU Massachusetts State Council and co-chairman of Raise Up Massachusetts. The coalition of community, religious, business, and labor union leaders spearheaded the successful 2014 initiative petition drive for earned sick time, which passed by an overwhelming margin.

“What the public has been telling the advocacy community and the Raise Up folks is that people understand the need for money, especially for education and transportation,” Kaufman says. “There is no implicit opposition to being wealthy. It is just a requirement that if you are that wealthy, you pay your fair share.”

Kaufman and his allies are hoping that heightened awareness of the growth in income inequality — and the fact that the measure only raises taxes on the millionaires’ club — will mean a different outcome than past efforts to enact a graduated state income tax.

Though the federal tax code imposes higher tax rates on higher earners, Massachusetts voters have resisted calls to get rid of its flat tax rate five times, the last in 1994, the year Kaufman was first elected to the Legislature.