No. 9, 1969). Land reform and the 1988 constitution The constitution now in effect, passed in 1988, requires that "property shall serve its social function" and that the government should "expropriate for the purpose of agrarian reform, rural property that is not performing its social function." Under Article 186 of the constitution, a social function is performed when rural property simultaneously meets the following requirements: Rational and adequate use. Adequate use of available natural resources and preservation of the environment. Compliance with the provisions which regulate labor relations. Development uses which favor the well-being of owners and workers. Since the criteria are vague and not objectively defined, the social interest principle was seen as a mixed blessing, but accepted in general. Landowners have lobbied against the principle since 1985 through the landowners' organization, União Democrática Ruralista (Democratic Union of Rural People, or UDR), whose rise and organization parallels that of the MST. Although it avowedly dissolved itself in the early 1990s, some believe it persists in informal regional ties between landowners. UDR lobbying over the constitutional text is believed to have watered down concrete enforcement of the "social interest" principle. One Brazilian law handbook argues that land reform, as understood in the 1988 constitution, is a concept made up of various "compromises" on which constitutional law has consistently evaded taking a clear stance, and so one could argue either for or against the MST without leaving the framework of the Constitution. The lack of clear government commitment to land reform precludes the MST engaging in public-interest litigation, so concrete proceedings for land reform are left to the initiative of the groups concerned, through onerous and time-consuming legal proceedings. Given "the highly problematic and ideologically driven nature of the Brazilian justice system". all parties have an incentive to resort to more informal methods: "while the large landowners try to evacuate squatters from their land, squatters might use violence to force institutional intervention favoring them with the land expropriation afterwards [...] violence is mandatory for both sides to achieve their goals". These tactics raise controversy about the legality of the MST's actions, since it tries to ensure social justice unilaterally. The MST identifies rural land it believes to be unproductive and that does not meet its social function, then occupies the land, only afterwards moving to ascertain the legality of the occupation. The MST is represented in these activities by public interest