Huge protests have taken place in several Mexican cities in response to what protesters claim are government attempts to undermine electoral authorities.

The largest was in Mexico City, where 500,000 people marched on the city's main plaza, according to organizers. According to the local government, the figure is 90,000.

Last week, lawmakers voted to reduce the National Electoral Institute's (INE) budget and staffing.

The INE is partisan, according to President Andrés Manuel López Obrador.

Opponents, however, see the recent vote as an assault on democracy itself and are urging the Supreme Court to overturn it as unconstitutional.

Massive crowds gathered in Mexico City's historic Zocalo Square on Sunday. Demonstrators spilled into adjacent streets in the city center.

"We're fighting to defend our democracy," protester Veronica Echevarria told Reuters. She was wearing a cap with the words "Hands off the INE" on it. Many protesters carried placards with similar slogans.

Smaller peaceful protests were held in a number of other cities.

The reforms were approved by Mexico's Senate on Wednesday, following a similar vote in the lower chamber of parliament. The reforms will go into effect once President López Obrador signs them.

According to Will Grant, the BBC's Mexico correspondent, it is possibly the most divisive political issue in Mexico right now.

López Obrador, who was elected in July 2018 after two previous failed attempts, has long been critical of the INE, the organization in charge of elections.

Last month, he accused the independent body of cheating, and said its staff turned a blind eye to "the stuffing of ballot boxes, the falsification of [election] records, and vote buying."

In his first run for president, in 2006, he was defeated by conservative rival Felipe Calderón by less than one percentage point. López Obrador refused to recognize the result, which he called fraudulent, for months.

He also challenged the outcome of the 2012 election, in which he was defeated by Enrique Pea Nieto.

López Obrador has been advocating for a reform of the INE that he claims will save taxpayers $150 million (£125 million) per year by drastically reducing the agency's staff.