(a) Any properly registered and qualified vendor who supplies services or commodities to any county, or agency thereof, shall be entitled to prompt payment upon presentation to that county or agency of a legitimate uncontested invoice.
(b) (1) Except as provided in subdivision (2) of this subsection, for purchases of services or commodities made on or after July 1, 1995, a check shall be issued in payment thereof within sixty days after a legitimate uncontested invoice is received by the county or agency receiving the services or commodities. Any check issued after such sixty days shall include interest at the current rate, as determined by the State Tax Commissioner under the provisions of section seventeen-a, article ten, chapter eleven of this code, which interest shall be calculated from the sixty-first day after the invoice was received by the county or agency until the date on which the check is mailed to the vendor: Provided, That this section shall not apply if payment cannot be made within the sixty-day period because of unforeseen budgetary constraints.
(2) For purposes of this subsection, an invoice shall be deemed to be received by a county, or agency thereof, on the date on which the invoice is marked as received by the county or agency, or the date of the postmark made by the United States postal service as evidenced on the envelope in which the invoice is mailed, whichever is earlier, unless the vendor can provide sufficient evidence that the invoice was received by the county or agency on an earlier date: Provided, That in the event an invoice is received by a county, or agency thereof, prior to the date on which the commodities or services covered by the invoice are delivered and accepted or fully performed and accepted, the invoice shall be deemed to be received on the date on which the commodities or services covered by the invoice were actually delivered and accepted or fully performed and accepted.