The former Morrison government finalised the loan with GB Energy in March earlier this year, for the Golden Beach gas production and storage project, offshore from Gippsland.
More than 1700 jobs are estimated to be supported by the project, which was granted in a bid to help alleviate gas shortfalls in the east coast market.
Greens resources spokeswoman Dorinda Cox will on Monday move a disallowance motion in the Senate to block the commercial loan.
"Labor can't criticise gas corporations one day, then hand out public money the next," she said.
"Real climate action in Victoria means stopping new coal and gas projects from the 12 Apostles to Gippsland, and that is what the Greens will do."
The International Energy Agency has said no new oil and gas projects should be developed if the world is to limit global warming to 1.5C and avoid its worst impacts.
Greens Leader Adam Bandt said Labor couldn't keep backing new coal and gas projects.
"The big gas corporations are making giant profits and the public shouldn't be on the hook for a new gas project that will make the climate crisis worse," he said.
"Labor needs to work with the Greens to ditch this terrible Morrison decision to back more gas."
Prime Minister Anthony Albanese has said the government will make an announcement before Christmas, as it considers a price cap on gas to help Australians with soaring energy prices.
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