Peru's electoral council has blocked the candidacy of the main challenger to front-runner Keiko Fujimori in April 10 presidential elections.
The body voided the candidacy of economist Julio Guzman's by a vote of 3-2. It cited technical reasons that many Peruvians have criticized as petty.
Guzman's spokesman, Daniel Mora, called the ruling "a stain on the electoral process."
Peru's institutions are still weak and corruption-riddled two decades after the autocratic rule of Fujimori's father, Alberto.
Guzman had surged in opinion polls that show him now preferred by about 17 percent of voters behind 35 percent for Keiko Fujimori, whose father is imprisoned for corruption and authorizing death squads.
If that held, he would have faced Keiko Fujimori in a June 5 runoff.