MEXICO CITY (AP) — Mexican President Andres Manuel Lopez Obrador has signed an open letter promising to not seek re-election after his six-year term ends in 2024.

That move was prompted by opposition fears that a proposal to let voters oust the president midway through his term might actually end up letting him serve longer.

The president's supporters in Congress advanced legislation last week that would call a referendum halfway through presidential terms — an idea Lopez Obrador had campaigned on.

But critics suspect it could undermine Mexico's constitutional prohibition on re-election. Conservative opponents have long compared Lopez Obrador to Venezuela's late Hugo Chavez and other leaders of the Latin American left who made moves to extend their time in office.

Lopez Obrador said Tuesday that in 2024 he'll retire to his ranch.