Nassau’s financial control board put a damper on county and state plans to quickly reimburse seniors for the costs of an expired tax abatement, warning Friday that lawmakers could not use county reserves to pay the estimated $7.1 million refund.

Adam Barsky, chairman of the Nassau Interim Finance Authority, told County Executive Edward Mangano and county legislators in a brief letter that they would have to cut expenses or raise revenue to repay some 44,000 Nassau seniors who lost an average $166 property tax break this year.

County officials had said they would finance reimbursement from Nassau’s $160 million fund balance, which exceeds by $20 million the county policy of holding 4 percent of its budget in reserves.

But Barsky wrote that dipping into the fund balance would exacerbate Nassau’s budget deficit. NIFA has projected the budget gap at $106 million this year, using generally accepted accounting practices, which do not allow proceeds from borrowing to be counted as operating revenues.

NIFA had directed that the deficit for 2017 not exceed $60 million.

“If our directive is not followed, NIFA will be forced to impose a budget modification that accomplishes this requirement,” Barsky said.

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Mangano, who is fighting unrelated federal corruption charges, did not respond to a request for comment Friday.

But Presiding Officer Norma Gonsalves said in a statement, “After forcing the County to overfund its rainy day fund, it is unconscionable that the unelected bureaucrats at NIFA would deny this benefit to vulnerable senior citizens.”

The popular abatement on county taxes was enacted in 2002 by the state at Nassau’s request to offset a 19.2 percent county property tax hike that year. It gave tax breaks to homeowners aged 65 or older with incomes under $86,000. Lawmakers gave no advance notice when the abatement expired last year.

County and state lawmakers since have filed bills to restore the abatement and also to reimburse those who lost the breaks this year.

Nassau did not have to budget for the abatement when it was in effect. The county collected the same amount of taxes, it just distributed the tax burden differently. Nonsenior homeowners paid a little more to make up for seniors paying a little less.

Going forward Nassau also will not have to budget for the abatement because the tax burden again will be redistributed.

But reimbursement for this year’s expired abatement creates a problem because tax bills have already gone out. The county cannot go back and hike the bills for nonseniors but must find the money itself.

Minority Leader Kevan Abrahams (D-Freeport) said Friday, “It’s disgraceful that the administration failed to budget for the renewal of the senior tax abatement and we will do everything we can to protect our senior citizens.”