The battle for Kevin Rudd's seat has become personal, with his replacement candidate trading barbs with Foreign Minister Julie Bishop about their work histories.
Ms Bishop was in the Brisbane-based seat of Griffith on Wednesday campaigning with Liberal National Party (LNP) hopeful Bill Glasson.
She fired the first salvo at Labor's Terri Butler, calling into question her history of union-related work after this week's allegations of criminal originations involvement with trade unions and the building industry.
"Bill Glasson's opponent is of the union movement," she told reporters.
"A former union organiser, a former union lawyer, she will have to toe the Labor Party line, and that is to prevent there being a proper inquiry into illegal, corrupt activities deep within the Labor movement."
But Ms Butler fired back, saying Labor had already implemented comprehensive union accountability laws and suggested Ms Bishop should worry about her own work history.
"Julie Bishop might want to talk about me being a union lawyer, but if she's a lawyer who has defended companies in respect of asbestos claims, I think perhaps she should think about whether she's prepared to talk about what her employers do," Ms Butler said.
"The allegations are about unions and employers, it's time we saw some balance from this government."
Ms Butler had her own heavyweight campaign support in the electorate in the form of opposition infrastructure spokesman Anthony Albanese, who criticised the government's efforts on public transport.
Prime Minister Tony Abbott will be in Griffith on Saturday to officially launch Dr Glasson's campaign in the lead up to the February 8 poll.
Dr Glasson defended suggestions Mr Abbott had previously been "airbrushed" from his campaign material due to bad polling.
"The only person being airbrushed from this campaign is Kevin Rudd," he said.
"The only reason we're having this election is because of Mr Rudd - a man who promised to serve his full three-year term, a man who promised the world and delivered Christmas Island."
Mr Rudd defeated Dr Glasson on preferences during last year's general election, but later announced his retirement from parliament after the coalition came to power.
Sportingbet has given the by-election to Ms Butler, saying her odds have shortened from $1.55 to $1.10, while Dr Glasson's have ballooned from $2.40 to $6.