Labor is seeking to pull off a second unlikely by-election win in a safe Liberal seat, having won Aston in Victoria against the odds in April.
The July 15 poll in Fadden was triggered by the resignation of former Liberal minister Stuart Robert, who has been mired in controversy.
The LNP holds the seat by a margin of 10.6 per cent and has chosen Gold Coast councillor Cameron Caldwell as its candidate.
Australian Electoral Commission state manager Stephanie Attard urged voters to carefully consider their personal circumstances when choosing whether to cast an early vote.
"Early voting centres are open in Helensvale and Runaway Bay from today with six early voting centres available from this weekend, and 29 open on by-election day."
Prime Minister Anthony Albanese launched the campaign for Labor's pick, nurse educator Letitia Del Fabbro, on the Gold Coast last week.
Nationals MP Barnaby Joyce said voters were concerned about the rising cost of living over other issues.
"The people of Fadden are not going to go to the polling booths thinking about Mr Robert - they're going to be thinking about power prices, they're going to be thinking about a government that's more focused on constitutional change than the cost of living," he told Seven's Sunrise on Monday.
Labor frontbencher Tanya Plibersek said it would be a tough election to win.
"Of course we are laser focused on (cost of living)," she told Sunrise.
The electoral commission has so far received 16,345 applications for postal votes.
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