Bill Shorten rebuffed an invitation to catch up with Rupert Murdoch in January and also passed on the opportunity to meet this month after the media mogul flew into Sydney with son Lachlan.

But the Opposition Leader has no such qualms about breaking bread with Anthony Pratt, Australia's richest man and generous political benefactor.

Labor leader Bill Shorten walks in to a Sydney apartment tower for lunch with billionaire Anthony Pratt. Louie Douvis

On the second day of the federal election campaign - having toured the Ryde Medical Centre in the Liberal electorate of Bennelong with health spokeswoman Catherine King and Labor senator Kristina Keneally - Shorten made a detour to Pratt's Sydney luxury apartment overlooking Circular Quay and Sydney Harbour.

He was there for lunch with the cardboard box king who, according to the Australian Financial Review, has a net worth of $12.9 billion.

The Pratt family is no stranger to Australia's political class. Pratt and his mother Jeanne hosted fundraisers for both the Labor and Liberal parties at their Melbourne mansion Raheen earlier this year.

On that occasion, Shorten brought along deputy leader Tanya Plibersek to mingle with corporate heavy-hitters including former Tennis Australia chair Harold Mitchell and Ellerston Capital chief Ashok Jacob.

Opposition Leader Bill Shorten swung through Sydney's affluent eastern suburbs on Friday morning. Alex Ellinghausen

The man opinion polls predict will be Australia's next prime minister is no stranger to the Pratts. As former prime minister Malcolm Turnbull likes to point out, Shorten was very friendly with Pratt's father, Richard, who died in 2009.

Indeed, Turnbull, a multi-millionaire who is partial to French bubbles, used to goad Shorten about "knocking back Dick Pratt's Cristal". Back then he was familiar with the inside of Dick Pratt's private jet.

During the last election, Pratt shelled out almost $800,000 for Turnbull's campaign.

This time, it is a more bipartisan effort - he's also hosted a fundraiser for Prime Minister Scott Morrison and the Coalition.

Anthony Pratt has hosted Bill Shorten twice in the last month. Luis Enrique Ascui

And as one Labor staffer put it: "Someone's got to pay for the fliers".

The Liberals aren't calling it quits on the fundraising effort either. This Sunday, South Australian Premier Steven Marshall and Victorian Liberal leader Michael O'Brien are coming together for a special federal election campaign money-making lunch in Melbourne, price undisclosed, but only two tickets remaining.

A few days later, outgoing Jobs Minister Kelly O'Dwyer makes her contribution to her replacement in Higgins, the Liberal candidate Katie Allen, with a one-off $195-a-head cocktail function.

"Selling out fast," as they say.