The proposed reform of Mexico's judiciary threatens the country's democracy and its vital trade relationship with the United States, U.S. Ambassador to Mexico Ken Salazar said Thursday.
The controversial reform, set for a congressional vote in September, proposes that judges, including all Supreme Court justices, be elected by popular vote.
"Based on my lifelong experience supporting the rule of law, I believe popular direct election of judges is a major risk to the functioning of Mexico's democracy," Salazar said in a statement.
The comments are by far the strongest made to date by Mexico's largest trading partner and represent a significant ratcheting up of tensions between the two countries over the issue.
Incoming President Claudia Sheinbaum, who takes office in October, has defended outgoing President Andres Manuel Lopez Obrador's judicial proposal, saying she agrees judges should be elected.
Salazar said the debate around the reform, and the politics of the process, were it to be approved, would threaten the U.S.-Mexico trade relationship, "which relies on investors' confidence in Mexico's legal framework."
"Any judicial reform should have the right kinds of safeguards that will ensure the judicial branch will be strengthened and not subject to the corruption of politics," he added.
Salazar said the reform could make Mexico's judiciary more vulnerable to influence from organized crime.
"Direct elections would also make it easier for cartels and other bad actors to take advantage of politically motivated and inexperienced judges," he said.
Mexico's presidency and foreign ministry did not immediately respond to a request for comment.
Lopez Obrador argues the reform, which proposes that judges be elected via votes in 2025 and 2027, will help combat impunity and corruption.
But markets have been on edge since Lopez Obrador's Morena party won an even greater chunk of congressional seats than forecast in a June national election, effectively guaranteeing it the ability to pass constitutional reforms when the new Congress takes office next month.
Mexico's stock market and peso currency were both down about 1% on Thursday.