Nassau’s financial control board on Wednesday threatened to reject the county’s 2017 budget and impose its own spending cuts if county legislators move forward with a plan trying to collect more than $35 million in penalties from a law that is under court challenge.

Adam Barsky, chairman of the Nassau Interim Finance Authority, said the budget-balancing plan offered by the legislature’s Republican majority was “unlikely to be realized.”

Lawmakers are hoping to generate the new revenues by allowing businesses to pay partial fines for not properly reporting their income and expenses.

“If the budget relies on these revenues, NIFA will reject it and immediately send it back to you for a speedy modification,” Barsky wrote to legislative leaders.

“If the necessary charges are not made and presented to NIFA, we are prepared to impose a budget that removes at least $36 million in authorized expenditures,” he said.

Barsky said NIFA would go as far as rejecting all contracts and borrowing requests contained in next year’s $2.9 billion spending plan.

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The letter came in response to GOP budget amendments to reduce an unpopular “public safety fee” proposed by County Executive Edward Mangano to fund new police hiring.

Lawmakers are set to vote Monday on reducing the planned $105 surcharge on traffic tickets to $55 and eliminate it for parking tickets. They’ll also vote on the fine-collection plan to replace the revenue.

“NIFA’s threat to shut down government and risk the health, safety and welfare of all Nassau County residents over a perceived gap that constitutes .01 percent of the county budget is outrageous,” Presiding Officer Norma Gonsalves (R-East Meadow) said in a statement Wednesday. “Yet we will continue to work with all our partners in government to improve Nassau’s finances.”

Between $36 million and $38 million would be lost from trimming the ticket surcharges, officials say. To recoup that revenue, legislative Republicans propose “partial amnesty” for businesses that haven’t complied with the county law requiring timely reporting of their finances.

The 2013 law is under challenge, and the Appellate Division of State Supreme Court is expected to hear the case next year.

Even before legislators reduced some fee revenues, NIFA had told county leaders to trim the projected 2017 budget deficit by $40 million.

Noting the amnesty program and the ticket fees, NIFA member Chris Wright said, “Relying on two uncertain sources of revenue to fund sure and certain expenses is doubling down on a deficit-inducing fiscal approach.”

A spokesman for Mangano declined to comment on NIFA’s letter.

Minority Leader Kevan Abrahams (D-Freeport) said this week that he thought the majority’s reliance on the amnesty program was “a little shaky.”

“Ultimately, I have very grave concerns,” he said. “We should not be using that to balance the budget.”

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NIFA in recent years has regularly reminded the county of its ability to make spending cuts. But the control board has yet to take such a step.

Last year, NIFA approved Mangano’s budget on the condition the county produce quarterly reports tracking whether revenue and spending estimates were on target.