Voting has opened for more than 41,000 constituents in the May 16 by-election in the north Brisbane seat of Stafford, which was sparked by the sudden death of MP Jimmy Sullivan on April 9.
The Greens declared on Tuesday they would not be allocating preferences, advising voters to put their candidate Jess Lane first and to number every box thereafter.
But Kos Samaras, director of political research company RedBridge, said the move was likely to backfire on the minor party.
"Greens voters are extremely discerning," he told AAP.
"They will purposely follow their own convictions across the country."
Mr Samaras said that preferences from Greens voters to Labor rarely varied, except in seats with high-profile independent campaigners or alternative left-wing options.
Even then, preferences eventually flowed back to Labor.
Greens MP Michael Berkman, who holds the inner west seat of Maiwar, said Queenslanders were being left behind while accusing both major parties of being in the pocket of corporate donors.
"If people want real change in Stafford they should vote 1 Greens then number every box," he said.
"No matter whether Stafford voters elect a Labor or an LNP politician, the cost of housing will keep going up.
"Both Labor and the LNP take the same dodgy corporate donations so it should be no surprise that under both LNP and Labor governments, Queenslanders' lives get harder while corporate profits soar."
Mr Samaras, an ex-Labor strategist, said the decision had the potential to hurt the Greens.
He said progressive voters were anxious about the rise of One Nation and, by extension, the LNP as the traditional conservative party tried to fend off attacks on its right flank.
"The message the Greens are sending is actually one that inflicts some personal damage on their brand," he said.
Sullivan, who had held the seat since 2020, had a margin of more than five per cent, and had been sitting on the crossbench after being expelled from the Labor Party in 2025.
The seat has traditionally been safe for Labor and was held by Mr Sullivan's father Terry from 2001 to 2006.
Opposition Leader Steven Miles was angry when he addressed reporters about the issue on Monday.
"I think Greens supporters would expect their political party to do absolutely everything they can to stop the LNP getting an additional seat," he said.
He said an open ticket would be an effective endorsement of the LNP's policies.
"It would be like the Greens' political party endorsing the ban on pill testing, endorsing the ban on gender treatment for trans kids, endorsing the government's move to criminalise homelessness," he said.
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