Opponents say the overhaul risks removing checks and balances on the ruling Morena party, by appointing judges friendly to their cause, and also allowing organized crime groups greater influence over the judicial system by running their own candidates.
Mexico joins Bolivia as the only countries worldwide to conduct judicial elections at the national level, though state-level judicial elections are common in the United States and some local Swiss judges are also elected.
Voters on Sunday will cast ballots for Mexico's nine Supreme Court judges, as well as for judges and magistrates across 19 of Mexico's 32 administrative divisions. More than 7,700 candidates are running for judicial posts.
Pollsters expect a poor turnout, in part due to opposition calls to boycott the vote, but also because of the complexity of the process and vast number of candidates to consider.