Anthony Albanese has fired the starting gun on a Labor leadership contest, the coalition says.
But Labor emphatically denies any rift between the former 2013 leadership contestant from the Left and the man who defeated him, Bill Shorten.
Mr Albanese delivered the Whitlam Oration on Friday night,l in which he set out an agenda for reforming the ALP and broadening the party's appeal to non-unionists and the business sector.
"Labor doesn't have to agree with business on issues such as company tax rates, but we do have to engage constructively with business large and small," he said.
Liberal frontbencher Christopher Pyne said Mr Albanese had directly contradicted Mr Shorten's "war with business" approach and placement of unions at the centre of public policy.
"Anthony Albanese has fired the starter gun on the Labor Party leadership contest," Mr Pyne said in Adelaide.
The cabinet minister, who regularly makes media appearances with Mr Albanese, said Mr Shorten's leadership had failed.
"We know where it's going to end, it will end in a ballot of the Labor Party membership and the caucus, and the sooner Bill Shorten gets on with it the better," he said.
Labor is contesting five by-elections on July 28, aiming to retain the seats of Braddon, Fremantle, Perth and Longman and pick up Mayo in South Australia.
The government's parliamentary win on personal income tax cuts could give Liberal candidates a popularity boost.
There has been speculation if Labor loses one or two seats there could be pressure on Mr Shorten's leadership.
Mr Pyne said there was "absolutely no expectation" the Liberals would win any of the by-elections, but if Labor lost it would put its leader "in very serious strife".
Labor deputy leader Tanya Plibersek said the party was focused on policy not personalities.
"Bill Shorten is a fantastic leader of the Labor party," she said.
"We've never been stronger and more united than we are under Bill's leadership. We've got fantastic policy out there. We've got fantastic people."
She said the Liberals had been focused on themselves and marked down for it.
Labor has led the coalition in more than 30 consecutive Newspolls.