At any time after the annual appropriations for the ensuing fiscal year are made by a city or town or by all the member cities and towns of a regional school district, a school committee may order materials, supplies and equipment and may contract for services for the public schools which are chargeable against such appropriations; provided, however, that payment may be made prior to the commencement of said ensuing fiscal year.
Mass. Gen. Laws ch. 71, § 49A