A national consultation on President Augusto Pinochet's political program was held throughout Chile on 4 January 1978. After being accused of human rights violations by the United Nations, Pinochet announced a national vote to confirm support for his policies. The 'yes' field of the ballot featured a Chilean flag, while the 'no' field featured a solid black rectangle to nudge the vote in favor of Pinochet.
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Text from the Wikipedia article “Chilean national consultation”, available under CC BY-SA 4.0.