Mexican President Andres Manuel Lopez Obrador on Tuesday asked the Senate for a referendum on whether to prosecute five of his predecessors over allegations including corruption.
Lopez Obrador's proposed "people's consultation" targets Carlos Salinas, Ernesto Zedillo, Vicente Fox, Felipe Calderon and Enrique Pena Nieto, whose terms in power stretched from 1988 to 2018.
He accused them of presiding over "excessive concentration of wealth, monumental losses to the treasury, privatization of public property and widespread corruption."
Calderon quickly hit back, saying Lopez Obrador "is mistaking the Republic for a Roman Circus."
"Instead of going to the prosecution with evidence, he asks the crowd whether to convict or pardon innocents, showing a thumb up or down," he wrote on Twitter.
"A setback to thousands of years of justice."
Under Mexican law, the president has the right to request a referendum, and it is up to the Supreme Court to decide whether it is constitutional.
Lopez Obrador proposed holding the referendum on June 6, 2021 to coincide with legislative elections.
He has used his daily appearances in front of the media in recent weeks to highlight allegations against his rivals made by Emilio Lozoya, a former advisor to Pena Nieto.
Lozoya, the ex-head of state oil giant PEMEX, has implicated Pena Nieto, Calderon and Salinas during his corruption trial linked to Brazilian construction giant Odebrecht.
Lopez Obrador, a left-wing populist who came to power in 2018 vowing to clean up the graft-riddled country, has called on his predecessors to testify in court.
But he has been accused by Calderon of using Lozoya "as an instrument of revenge and political persecution."
Mexico is considered one of the world's most corrupt countries, ranked 130 out of 180 in Transparency International's Corruption Perceptions Index.
Lopez Obrador has overseen a series of referendums since taking office on controversial issues including his "Maya Train" railroad project and canceling a partially finished airport for Mexico City.