The reform's approval by lawmakers last year knocked financial markets, sparked the United States to express concern about a weaker judicial system, and sparked a strike by the country's judicial workers.

"Mexico's justice system was far from perfect, and this new judicial system will not address its shortcomings," said Rodolfo Ramos, an analyst at Brazilian bank Bradesco BBI.

Ramos said "the real litmus test" would come when cases against a government action reach the Supreme Court.

Counting is expected to take two weeks, with the results out on June 15.

In 2027, another vote is scheduled to fill over 1,000 more judicial positions.