The period of Gierek's rule is notable for the rise of organized opposition in Poland. Changes in the constitution, proposed by the regime, caused considerable controversy at the turn of 1975 and 1976. The intended amendments included formalizing the "socialist character of the state", the leading role of the PZPR and the Polish-Soviet alliance. The widely opposed alterations resulted in numerous protest letters and other actions, but were supported at the VII Congress of the PZPR in December 1975 and largely implemented by the "Sejm" in February 1976. Organized opposition circles developed gradually and reached 3000–4000 members by the end of the decade.