Gov. Andrew M. Cuomo, seen here on Tuesday, had said...

Gov. Andrew M. Cuomo, seen here on Tuesday, had said he would sue the president over the federal income tax plan. Credit: Howard Schnapp

ALBANY — It’s been seven months since Gov. Andrew M. Cuomo promised to sue President Donald Trump over the federal income tax plan Trump signed in December.

But Cuomo still hasn’t filed a claim.

A Cuomo aide said Thursday the lawsuit is coming, and that the delay is due, in part, to coordination with other states that might join the fight.

“We’re finalizing papers in the other states and will be moving forward in the near future,” Cuomo spokesman Rich Azzopardi said in an email.

Some have expressed doubt about whether New York has grounds to sue over the tax plan. Specifically, Cuomo says the tax law treats “blue” states unfairly regarding limitations on federal deductions.

“If he files it, it’s going nowhere,” said E.J. McMahon of the Empire Center, a conservative-leaning, Albany-based think tank that reviews state policies and finances.

“You don’t have to be a lawyer to figure he doesn’t have a leg to stand on,” McMahon said. “There is ample precedent for restricting or capping any itemized deductions.”

Cuomo, a Democrat who is up for re-election and faces a primary challenge from Cynthia Nixon, said the Trump-backed plan pits rich versus poor.

Further, he argued that an element of the plan that limits federal deductions a taxpayer can take for state and local taxes unfairly targeted high-income, high-tax states such as New York, California and Illinois — all “blue,” or primarily Democratic states.

The limit on state and local tax deductions (known as “SALT” in government circles) amounted to “double taxation,” Cuomo said, and clearly was aimed at punishing states led by Democrats. That violates the “equal protection” guarantees is the Constitution, according to Cuomo.

The governor vowed to sue in December and reinforced the promise by making it the keynote of his 2018 State of the State address in January, garnering front-page headlines around the state.

“We believe it is illegal and we will challenge it in court as unconstitutional,” Cuomo said to applause from Democratic state lawmakers.

In April, when Cuomo signed a law that could reduce the impact of the SALT limitation for some high earners, aides said the federal lawsuit could be filed soon.

Then, they indicated it likely would be filed the first week of June.

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