New Jersey Gov. Phil Murphy is still trying to tax his way out of a huge budget hole to avoid upsetting the public unions who are his biggest supporters. It’s up to his fellow Democrats to tell him no again.

In Tuesday’s budget message, Murphy will propose lowering the income threshold for the state’s top income tax rate of 10.75 percent to kick in from $5 million to $1 million. The rate now hits just 1,760 taxpayers; the gov’s plan would boost it to some 39,000.

Murphy wants new cash to pay for even more government spending, which grew 8 percent last year; his hike adds an estimated $447 million. And he says it’s still needed, though he’ll claim to have found $1 billion in spending cuts.

State Senate President Steve Sweeney and Assembly Speaker Craig Coughlin, both Democrats, refuse to consider new taxes without significant spending reforms, including to health and pension benefits for government employees.

Sweeney warns that, without the systemic cost-cutting he has proposed, “All you’re doing is continuing a cycle of every year taxing or finding new taxes so you don’t have to deal with the 800-pound gorilla in the room.

“The people who can leave are leaving,” Sweeney notes, because Jersey is already “overtaxed.” And 60 percent of its gross income tax revenue comes from the wealthiest taxpayers, who are the most mobile.

Indeed, state tax revenues for the current year are already falling short (up less than 3 percent when last year’s budget assumed they’d grow 7.5 percent), mainly because the income-tax take is down more than 5 percent from the year before.

Which means Murphy’s “tax the rich” approach, without serious genuine spending cuts, will soon lead to higher rates for the middle class, too.

Coming to grips with New Jersey’s fiscal mess requires painful decisions — not the fantasy that tax-and-spend can work forever.