Huge rallies have been held in several Mexican cities against what protesters say are government attempts to undermine the electoral authorities.
Lawmakers last week voted to slash the budget of the National Electoral Institute and cut its staffing.
President Andrés Manuel López Obrador accuses the INE of being partisan.
But opponents describe the recent vote as an attack on democracy, pressing the Supreme Court to overturn them as unconstitutional.
Massive crowds gathered in Mexico City's historic Zocalo Square.