The FCC modified local television ownership rules to allow tri-ownership in markets of 18 stations or more, and duo-ownership in all other markets, subject to a restriction on a combination of any of the four largest stations in any market. This change followed from a directive from the Telecommunications Act of 1996, in which Congress directed the FCC to examine its current rules which at the time prohibited common ownership of two stations with overlapping Grade B signal contours, known as the 'Single Market, Single Station Rule'.