Section 5 of Chapter 40A of the General Laws is amended by inserting in paragraph 5 the following after “in accordance with section 3 of chapter 40R.”:-

(5) an inclusionary zoning ordinance or bylaw. As used in this paragraph the term “inclusionary zoning” shall refer to zoning ordinances or by-laws enacted principally to ensure some provision of affordable housing in any residential subdivision or multi-unit residential project of a size to be determined by the municipality; provided, that a certain percentage of such subdivision or project’s dwelling units or net floor area, as determined by the municipality, shall be reserved for the construction of dwelling units permanently affordable for occupancy to persons whose household income does not exceed a municipally determined per cent of such municipality’s area median income as such income is determined by the federal department of Housing and Urban Development; and provided further, that the Executive Office of Housing and Livable Communities may issue guidelines or promulgate regulations consistent with this paragraph, including, but not limited to, provisions to ensure that such zoning ordinance or by-law shall not unduly constrain the production of housing.