Mexico’s former foreign minister Marcelo Ebrard, a leading contender to win the presidency next year, accused his own party leaders of trying to undermine his chances.

The bosses of the ruling Morena movement are running a “dark campaign” to favor former Mexico City mayor Claudia Sheinbaum, his main rival for the party’s nomination in next year’s election, Ebrard said Wednesday.

Morena chiefs are using party machinery to drive more attendees to Sheinbaum’s events than to his own, Ebrard told reporters in Mexico City.

“Why taint the process?” he said. “Let the people choose freely.”

Whoever wins the Morena nomination is likely to win the 2024 election, given the high popularity of incumbent President Andres Manuel Lopez Obrador.

The party is currently choosing a “national coordinator” for the campaign, who is also likely to be the nominee for president. This will follow a series of surveys whose details still aren’t clear, with the final decision to be announced on Sept. 6.

Favorite Contender

Sheinbaum is widely perceived as Lopez Obrador’s “favorite contender,” Citigroup Inc. analysts Ernesto Revilla and Nydia Iglesias said in a report this week.

On Wednesday, while campaigning in Michoacan state, Sheinbaum told reporters the accusations are false.

“We would never do that. All the support has been voluntary and self-motivated,” she said, in an audio sent by her press office. “You’ll never hear me speak ill of any of my colleagues.”

Ebrard said that he is the favorite to win, which is why the process has become biased against him. The pollsters that will participate in the survey process will be announced on Aug. 17.

Read More: Mexico’s Sheinbaum Grows Advantage in Nomination Race, Poll Says

The opposition, currently going through a similar process, is due to announce its candidate on Sept. 3. Officially, campaigning for the presidency in Mexico doesn’t start until 2024.

(Updates with response from Sheinbaum in sixth paragraph.)