The CFMMEU helped the Coalition win two key seats back from Labor at the May election by funding the campaigns of two independents who sent 1757 votes between them to the Liberal Party.
Recreational fishermen Todd Lambert and Brett Smith were approached by the Construction, Forestry, Maritime, Mining and Energy Union to run in the Tasmanian battleground seats of Bass and Braddon, with their campaigns fully funded by the union, which donated $43,718.
Despite putting Labor second in their how-to-vote cards - after securing a pledge from Bill Shorten to ban supertrawlers, which locals fear will deplete fish stocks - almost half of the pair's preferences went to Liberals Bridget Archer and Gavin Pearce.
Ms Archer won Bass by just 563 votes in the two-party preferred count with a 5.8 per cent swing. Of the 2607 people in the electorate who voted for Mr Lambert, 1237 did not follow the preference allocation on his how-to-vote card, instead helping elect Ms Archer.
In Braddon, Mr Smith - who received $15,509 from the CFMMEU - garnered 1203 votes, but 520 of them flowed to Mr Pearce, who won the seat by 4329 votes, a swing against Labor of 4.8 per cent.
The results helped restore the Coalition majority with two of the three net seats won in the May election.
The CFMMEU national office donated $28,209 to Mr Lambert, who told the Sydney Morning Herald and The Age he had "reluctantly" agreed to run for the seat of Bass in a bid to "get the best outcome" for recreational fishing.
"I was approached a couple of weeks out from the election," Mr Lambert said.
"It was a very short campaign, I had about 15 signs and a couple of radio ads and I still got just under 4 per cent of the vote ... It shows the recreational fishing vote is alive and well and we need the major parties to wake up to it."
The former Communications Union organiser said many Tasmanians were fed up with both major parties and fishing was a vote decider for tradesmen who fished.
"Most of us are tradies and what do we do, we buy boats and go fishing on the weekend," he said.
Mr Smith agreed, saying he had decided to run in Braddon to "stick up for recreational fishers" who "don't get listened to".
CFMMEU Tasmania organiser Kevin Harkins, who recruited the two independents, said the union's aim was to force both major parties to engage with recreational fishermen - many of whom were members.
"This was not vote harvesting," Mr Harkins said.
The CFMMEU has donated millions of dollars to the Labor party in recent years, but Victorian construction secretary John Setka has vowed to halt all donations from his branch in response to Labor leader Anthony Albanese's push to have him expelled from the party.
Mr Setka quit the ALP last month before the party's national executive was due to consider the motion to expel him on the grounds he had brought the party into disrepute.
Labor declined to comment.