From 1929 to 1997, the majority party and the only political group to gain national significance was the Institutional Revolutionary Party (Partido Revolucionario Institucional—PRI), formerly called the National Revolutionary Party (Partido Nacional Revolucionario), and the Party of the Mexican Revolution (Partido de la Revolución Mexicana). The PRI includes only civilians and embraces all shades of political opinion. Three large pressure groups operate within the PRI: labor, the peasantry, and the "popular" sector (such as bureaucrats, teachers, and small business people).
In the July 1997 elections, for the first time in nearly 70 years, the PRI failed to retain a majority of seats in the 500-member lower house of Congress, the Chamber of Deputies. Following the election, the PRI had 239 seats; the Party of the Democratic Revolution (PRD) had 125; 122 seats were controlled by the National Action Party (PAN); the Green Ecological Party (PVEM) had 8; and the Workers Party (PT) had 6.
Of the major opposition parties, the PRD advocates active government intervention in economic matters and questions close relations with the United States, while PAN favors a reduced government role in the economy, backs close ties with the United States, and is closely linked to the Catholic Church.
Vicente Fox, of the conservative PAN party, was elected on 2 July 2000, thereby ending over 70 years of PRI control. The PAN also became the largest party in the 500-member Chamber of Deputies, with 223 seats. In the Senate, the PRI won 60 seats in the 128-member Chamber. The PRD won 53 seats in the Chamber and 17 in the Senate. Thus, no party holds majority control on either Chamber of the Mexican Congress. The results of the 2003 midterm election were unlikely to change the divided composition of Congress.