While relatives of victims of the dictatorship, and even some judges, brought proceedings against the Supreme Court to declare the law unconstitutional, the National Pro Referendum Commission was started to collect signatures in order to enable a referendum that would nullify the articles 1 to 4 of Law 15,848. The Commission was chaired by Matilde Rodríguez Larreta, widow of legislator Héctor Gutiérrez, who was assassinated in Buenos Aires in May 1976.

The Commission also included Elisa Dellepiane, widow of Zelmar Michelini, who killed along with Gutiérrez Ruiz, and María Esther Gatti, grandmother Mariana Zaffaroni, who was kidnapped with her parents when she was just 18 months old in September 1976. The Commission included people from all areas and political sectors. It was decided that there was to be no direct representatives of the parties, because the group sought to prosecute those responsible for crimes committed during the dictatorship regardless of political affiliation. About 600,000 signatures (equivalent to 25% of the electorate at the time) were needed to enable the referendum.

The government harshly criticized the collection of signatures to enable the plebiscite. President Julio María Sanguinetti said the campaign was based on hatred and resentment. The ranks of the Colorado Party denounced the effort and claimed the initiative had arisen by part of the Tupamaros. Finally, in December 1987, shortly before the one year deadline provided in the Constitution for submission of signatures, the Electoral Court received about 635 thousand signatures, representing 28% of those in the electoral rolls. The questionable criteria put forward by the Court to nullify signatures, or, at best, leaving them subject to review, were denounced by the National Pro Referendum Commission. For example, signatures were discarded of people who had publicly stated their support for the annulment of the law. In any case, the Electoral Court announced that the signatures were sufficient and that there should be a plebiscite.

The plebiscite was to be held on 16 April 1989, and it was decided that the advocates of the nullification of the law would vote with a green ballot, while those who were inclined to confirm it, would vote with a yellow ballot. The campaigns for and against the law went along very different paths.

The Pro Referendum Commission appealed for equality. "(We all must) be equal before the law" was one of their slogans. With few resources, the Commission carried out a door to door and word of mouth campaign. Meanwhile, those who fought to maintain the law that gave amnesty to those responsible for human rights violations during the dictatorship did not follow a specific plan to convince the electorate, but used fear as their main weapon. President Sanguinetti said that overturning the law would lead to a "serious institutional risk," adding that "the victory of the green vote (...) would be a setback on the open road to the stability of democracy." Vice President Tarigo claimed that "there is no guarantee that those who were willing to disobey in 1986 will obey in 1989," and even former Army Commander Hugo Medina, then Minister of Defense, when asked about what would happen in the country if the law were annulled and the military had to be brought to justice, said: "we shall see", planting the seeds more of doubt than of certainty. On the other hand, the supporters of the yellow vote argued that if there had been amnesty for the Tupamaros, there also should be amnesty for the military. In fact, there had been no amnesty for the Tupamaros, since the authors of the so-called "blood crimes" had been tried by ordinary courts (as had been intended with the military).

On the other hand, most had already served years of imprisonment (in some cases more than a decade) and had undergone all sorts of harassment and torture. There were also those who wanted to "turn the page" and appealed for "peace." Sanguinetti, in recent remarks recalling that time, said he had prioritized "peace" over "justice."

The military, meanwhile, refused even to be pardoned, because they understood that they had done nothing to merit the "forgiveness" of society: "we participated in a war, and you can not judge the acts committed during a war with the laws of peace." Only the Tupamaros had stated firmly before the plebiscite that it would abide by the election result, "whether we like it or not,” said Tupamaro leader and current Senator Eleuterio Fernandez Huidobro. On 16 April 1989, citizens voted to confirm or annul Articles 1 to 4 of law 15,848. Almost 85% of the population voted. The 56.65% voted the yellow ballot and 43.34% voted for the green. The public had spoken in favor of maintaining a law that pardoned without question the murders, rapes and disappearances during the years of dictatorship. Journalist Guillermo Waksman asked, "how can we interpret the success of the yellow vote? What was the argument that was more successful? The one of equity, of resignation and helplessness, or of fear? Undoubtedly there was a mixture and the three factors contributed.

The next day the President of the Republic considered necessary to clarify that the outcome was not an endorsement of the actions of the armed forces during the dictatorship, let alone the procedures that we have all condemned at one time or another. There is a question: will the military think so? How will they interpret, from today forward, the fact that a majority has democratically decided to accept that there will be no prosecutions for killings, disappearances and torture?" The interpretations were many. First, all sectors of the right (from political groups to the media), noted that the vote was something of a gamble for peace, a "turning of the page" and not as an acceptance of the atrocities committed by the military, even though there was not, in fact, a willingness to judge the military for its role in the dictatorship.

Moreover, the important vote to annul the Amnesty Law, particularly in Montevideo, the only department where the green vote exceeded the yellow, confirmed that many people were seeking the truth above political affiliations and the facts proved in Montevideo was clearly more progressive than the interior. The Frente Amplio’s victory in the departmental elections following the plebiscite, was simply the demonstration that a change was brewing in the country's political mentality. Another significant finding, and that somehow also marked the near future following the referendum, was the high percentage of young people voting for overturning the law, unlike older voters, where a large majority preferred let things be as they were. In the coming national elections of 25 October, citizens will have another new opportunity to annul law 15,848.

Sources:

http://es.wikipedia.org/wiki/Ley_de_Caducidad_de_la_Pretensi%C3%B3n_Punitiva_del_Estado
http://www.espectador.com/text/documentos/doc05101.htm
PALACIOS, Santiago; El Presidente Sanguinetti cree que los militares “perdonados” no podrán ser juzgados de nuevo; La Vanguardia, Spain 15/4/1989, pg. 7
WAKSMAN, Guillermo; Uruguay: Consagración de la democracia tutelada; Nueva Sociedad, No. 102, July-August 1989, ppg. 13-19