Mexico’s Senate has approved a reform of the country’s electoral institute, a move that opponents say will undercut democracy but which the president contends will save money and reduce political privileges.

On Wednesday, lawmakers voted 72-50 in favour of the controversial overhaul of the body overseeing the country’s elections. Opponents immediately said they will challenge the changes in the Supreme Court. Protests are planned in multiple cities on Sunday.

The changes will cut the budget of the National Electoral Institute (INE), cull staff and close offices.

President Andres Manuel Lopez Obrador still needs to enact the measure, but that is seen as a formality since he backs the initiative, which would reduce the size of the institute and limit its supervisory and sanctioning powers.

The president proposed the legislative initiative, known as “Plan B”, in December after he did not get enough votes in Congress for a constitutional reform that included greater electoral changes.

The president has repeatedly denied that the reform package could pose a risk to elections, saying the initiative seeks to cut the INE’s large budget and end its privileges.

Lopez Obrador and his supporters have been critical of the institute since 2006, when he came within 0.56 percent of the vote of winning the presidency and denounced his loss as fraudulent. He and his supporters launched a mass protest movement.

Despite the institute confirming his landslide victory in 2018, Lopez Obrador has repeatedly complained about how costly it is to run elections in Mexico and sought to curtail the INE’s budget.

He frequently says that the independent body is in the hands of the elite.

Some Mexicans see similarities to the rhetoric used by former US President Donald Trump and ex-Brazilian President Jair Bolsonaro ahead of elections in those countries that aimed to erode confidence.

‘Key pillar’ of Mexico’s democracy

Many in Mexico see the electoral institute as a key pillar of the country’s modern democracy. After 71 years of uninterrupted single-party rule, the opposition finally broke through in 2000.

Lopez Obrador’s ruling Morena party is favoured in next year’s national elections, and the opposition is in disarray, which would seem to give the president little incentive to attack the electoral institute. He remains highly popular in Mexico but is not eligible for re-election.

Lorenzo Cordova, the institute’s leader, has aggressively defended it publicly and framed the reforms as threatening Mexico’s democracy. His outspokenness has made him a frequent target of Lopez Obrador.

After Wednesday’s vote, the institute said via Twitter that the reform “puts at risk the equity and transparency of the elections” by weakening the sanctions it can impose on candidates and parties that violate campaign finance rules.

Even before Wednesday’s vote, the opposition had called a march in Mexico City on Sunday in defence of the institute. The opposition held a similar march in November, which was ridiculed by Lopez Obrador, who led an even larger march days later.

The president had already worried some observers by frequently attacking the judiciary and concentrating enormous responsibility in the hands of the military, raising questions about his respect for the country’s democratic institutions.