The Nationals leader was on the wombat trail in Shepparton, Victoria, to announce a $146m rural health policy.

Mr Joyce was trying to answer the question of a local ABC journalist about the impact of a potential rate rise, when he was interrupted by the heckler, who yelled out "you're corrupt Barnaby" several times before being intercepted by Mr Joyce's Australian Federal Police protection unit.

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Mr Joyce labelled the man a union thug.

Moments early, in response to a question about why he was attacking independent candidates instead of investigating why Coalition voters were turning to them, Mr Joyce said independents were standing on issues that weren't high priorities for regional people.

"I ask these people, 'how important is ICAC to you?' They'll say 'what's ICAC?'," Mr Joyce said.

"But if I say to people 'how important is regional health and finding a doctor? They'll say 'incredibly important'.

"Others might say it's an important issue, but I'm going to go with experience."

Shepparton is located in Nicholls, a seat the Nationals hold with a 20 per cent margin.

Despite being the Nationals safest Victorian seats, the party has a fight on its hands to retain.

The retirement of MP Damian Drum has set the scene for a three-way battle between the Liberals, Nationals and independent candidate Rob Priestly, who is calling for a federal anti-corruption body.

The heckler claimed to be a patient at the medical facility where the announcement was being made, however staff didn't recognise him.