President Andres Manuel Lopez Obrador’s war of words with the plain-talking senator and former Indigenous affairs official Xochitl Galvez escalated to its highest level yet on Friday. He likened her to a mafia leader, and she accused him of illegally leaking confidential tax information about her businesses.

Lopez Obrador, who is barred from running again after the end of his six-year term, has spent weeks using his morning press briefings to criticise Galvez, who hasn’t been nominated yet but has been gaining momentum as an opposition-party candidate.

The complaints commission of the National Electoral Institute ruled late on Thursday that Lopez Obrador’s remarks “apparently violated the principles of equity [and] neutrality impartiality”. It ordered the president to “avoid commenting on electoral matters”.

But Lopez Obrador claimed on Friday that the electoral authorities “are trying to silence me” and violate his freedom of expression. He argued that, because his office had not been formally notified of the ruling, he could continue criticising Galvez.

“We still have time before they want to limit me,” Lopez Obrador said, repeating claims that Galvez was “the representative of the mafia of power” and that her company had received $88m in government contracts.

Lopez Obrador later amended that to claim Galvez’s companies had received $82m in government work. When Galvez denied that claim and challenged the president to prove it, he posted a link on Twitter that led to an unsigned document showing alleged totals of contracts.

The link was marked by Twitter as “spammy or unsafe”, but was not blocked.

Besides the government contracts — whose amounts Galvez disputed — the document also showed a series of contracts Galvez’s company allegedly had with private companies, as well as the firm’s payroll figures and bank deposits.

Those are figures that are normally only available to tax authorities. Mexican law normally prohibits the release of such information, with exceptions for things like court cases.

Galvez said the president’s post had used confidential government information and she would file a complaint.

“Mr President you have just put your foot in it,” Galvez wrote in her social media accounts. “With this tweet and the document, you have demonstrated that you are using all the power of the government to deceitfully investigate me because of my [political] aspirations.”

“You have violated a series of laws, and for that reason, I will take legal action against you,” she wrote.

It would not be the first time the president has appeared to use confidential government information like tax receipts to go after people he considers political foes.

In 2022, Lopez Obrador published a chart showing the income of Carlos Loret de Mola, a journalist who had written stories critical of the president.

The president initially alleged he got such information — which Loret de Mola has said is wrong — “from the people”, but he later said he based the chart in part on tax receipts, which would have been available only to the party who wrote them or the government tax agency.

Galvez has noted that even Lopez Obrador’s own administration has hired her information technology company to do government work, showing how good the firm is.

“The president is upset by tax-paying jobs and businesses because he has never seen one,” she wrote. “He is used to [getting money] in plain envelopes.”

Galvez is an independent who serves in the Senate for the conservative National Action Party. She comes from a small-town, partly Indigenous background and has often taken more progressive stances.

After decades in the 20th century in which the former ruling party used government funds to influence elections, Mexico passed strict rules in the late 1990s saying the government had to remain neutral in elections and not use public funds to support or oppose candidates.

Article 134 of the Constitution decrees that government media, advertising and public relations must only be used for informative or educational purposes, not for or against any politician. The government pays to produce and broadcast the morning press briefings, held at the lavish National Palace where Lopez Obrador lives.

For several decades, Mexican presidents have avoided — and in recent years, been legally prohibited from — making openly partisan campaign statements. That is, in part, because Mexico is a highly centralised country where the president wields enormous power, both political and financial.

Lopez Obrador’s behaviour could be compared with then-outgoing US President Barack Obama lashing candidate Donald Trump regularly and at length at White House press briefings in 2016, or George W Bush using such briefings to regularly attack Obama in 2008.

Parties are currently still in the primary season, and official campaigns for the June 2024 presidential elections do not formally start until September

Lopez Obrador has already run afoul of electoral courts on precisely this issue.

Earlier this year, a federal electoral tribunal ruled that Lopez Obrador had violated rules prohibiting the use of government resources in campaigns, related to comments he made during the run-up to two state elections held in Mexico in June.

In March, Lopez Obrador used his morning press briefing to urge Mexicans not to vote for opposition candidates in the two-state races, saying, “Don’t vote for the conservative Alliance … Not one vote for the conservatives.”

Galvez has asked to be allowed to respond to the president’s comments at the daily press briefing and even got a court injunction allowing her to do so. But Lopez Obrador refused, saying she wanted to “play politics” at the briefing.