In an attempt to require more affordable housing from luxury developers receiving tax breaks -- and responding to the efforts of advocates and tenants -- the City Council passed Local Law 58 in December 2006. The law required greater numbers of affordable units from those landlords claiming 421a tax benefits.
In June 2007, the state legislature expanded on this local law, including new outer borough neighborhoods in the "exclusion zone," the area within which affordable units must be included to receive the tax break. The state legislation requires that 20% of the units in these buildings be affordable to households at 60% of the area median income ($42,540 for a household of 4) and that units remain affordable for 40 years. Employees of these buildings must be paid at the City's prevailing wage.
For more information, and for a map of the exclusion zone, check out http://www.prattcenter.net/nyc421areform.php.