But the Australian Electoral Commission (AEC) would prefer voters ignored Mr Latham's advice and not waste their vote.
The controversial political figure, who has dogged both Prime Minister Julia Gillard and Opposition Leader Tony Abbott during the election campaign, used a report he prepared for the Nine Network's 60 Minutes on Sunday to spruik a protest vote.
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"When it comes to good ideas for Australia's future, Gillard and Abbott have given the voters a blank piece of paper," he said.
"I say let's give them a blank piece of paper in return."
While voting was compulsory in Australia, it was not compulsory to fill out the ballot paper, Mr Latham said.
"You can put it in the ballot box, totally blank.
"That's what I'll be doing on Saturday and I urge you to do the same. It's the ultimate protest vote."
An AEC spokesman confirmed to AAP that the Commonwealth Electoral Act did not contain an explicit provision prohibiting the casting of a blank vote, even though it was "obviously a wasted vote".
A provision of the act does prohibit a person printing, publishing or distributing "any matter or thing" that is likely to mislead or deceive an elector in relation to the casting of a vote.
Constitutional lawyer George Williams says Mr Latham's call was not misleading.
"But it could well be a problem legally to urge people to do otherwise than the thing they are lawfully required to do," he told the Herald-Sun newspaper.
The AEC says most informal votes - about four per cent of the total vote - were cast unintentionally.
"A tiny proportion are blank ballots," a spokesman said.
