MEXICO CITY (Reuters) - Struggling to kick-start his campaign and clean up the image of the graft-stained ruling party he hopes to lead to election victory, Mexican presidential hopeful Jose Antonio Meade on Friday proposed tougher anti-corruption legislation.

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Institutional Revolutionary Party (PRI) contender Meade, a longtime public servant with a reputation for decency, is polling in third place ahead of the July election, weighed down by the PRI’s record on corruption.

At an event in the Caribbean tourist resort of Cancun, Meade said his coalition would present a bill to impose tougher sentences on officials found guilty of corruption.

Under the initiative, the burden of proof would fall on officials suspected of corruption to show that their wealth was legitimate, or risk losing their assets, including properties registered in other people’s names, Meade said.

“The mechanism is simple: whoever cannot explain the origin of their assets will forfeit them to the state,” he said, according to a campaign statement.

The credibility of the PRI, which dominated Mexican politics for most of the past century, has been undermined by graft, and the fight against corruption promises to be a major issue on the campaign trail.

Several former PRI state governors are in custody facing charges ranging from embezzlement to drug trafficking and earlier on Friday the attorney general’s office said it had issued extradition requests for another PRI ex-governor.

In 2014, President Enrique Pena Nieto, his wife and a top aide all faced allegations of conflicts of interest over properties they acquired from government contractors, though a government-led probe exonerated them of wrongdoing.

Meade told supporters “the fight against corruption cannot wait,” and urged his rivals to support his initiative.

A former finance minister, Meade faces a delicate balancing act of persuading undecided voters he will cut out graft without alienating the PRI base he needs to win.

Meade’s nomination for the PRI ticket is not guaranteed, and rumors of discontent over his campaign have swirled in recent weeks, encouraging some speculation he may be ditched before the PRI formally elects its candidate on Feb. 18.

Presidential front-runner Andres Manuel Lopez Obrador, a leftist, has long railed against corruption. An opinion poll this week showed Meade losing ground to Lopez Obrador.

Meade delivered his remarks in the state of Quintana Roo, which was governed until 2016 by the PRI’s Roberto Borge. Earlier this month, Borge was extradited from Panama to Mexico to face corruption charges. Borge denies the charges.