BOSTON — Massachusetts Republican Party Chairman Jim Lyons is sounding the alarm on the Democrats’ newest scheme to unleash a graduated income tax system on the commonwealth, a proposal voters have previously rejected and the high court ruled was unconstitutional.

On Wednesday, Democrats are slated to advance the surtax proposal, a process that requires amending the Massachusetts Constitution.

Supporters of the measure claim it’s restricted to forcing the wealthy — who already pay the most in taxes — to fork over “their fair share.”

A closer look reveals Democrats want more. Three Democrats — Wellesley state Rep. Alice Peisch, Gloucester state Rep. Ann-Margaret Ferrante, and North Andover state Sen. Barry Finegold — want to dump the state’s constitutionally-protected flat tax system altogether.

Their amendment would abolish the “uniform rate,” meaning the Democrats would then be free to raise taxes on everyone.

“The same party that voted to give themselves a huge pay raise wants more of your money,” Lyons said. “This is a blatant cash grab masquerading as class warfare.”

A constitutional amendment is needed because the Massachusetts Constitution forbids a graduated tax system. Democrats say they want to earmark revenue generated by the new tax for transportation and education projects.

“We need to address spending first,” Lyons said. “For example, it costs Massachusetts seven times more than it does New Hampshire to build the same mile of roadway.”

The Democrats need yes votes from at least half of the state Legislature in successive sessions in order for the proposal to land on the November 2022 ballot. This week’s vote marks the first step. Another constitutional convention vote during the 2021-2022 legislative session will determine whether the proposal goes before voters.

“The tax is simply a bad idea,” Lyons said. “Massachusetts doesn’t have a revenue problem.

“It has a spending problem.”