The dwellings in public low-rent housing shall be available solely for families whose net family income does not exceed the maximum net family income falling within the lowest 20 percent by number of all family incomes in the area of operation as such maximum net family income has been determined by the authority. Each year, this restriction shall be reexamined by the commissioner of employment and economic development, and a public hearing shall be held by the commissioner of employment and economic development to determine whether administrative or interpretive difficulties or unsatisfactory progress in the provision of low-rent housing or redevelopment require a modification of that income restriction. Upon the conclusion of that hearing, the commissioner shall modify the restriction set out in this section to the extent required to make satisfactory progress in the provision of low-rent housing or redevelopment.