Billionaire pub baron Justin Hemmes’ generous offer to host a cocktail party to raise campaign cash for Scott Morrison is under fire from unions, who claim the hotelier has ripped off workers.

The Prime Minister is accused of preferring to “rub shoulders with billionaires” than workers after it emerged that Mr Hemmes will host a fundraiser next month at his Vaucluse mansion.

The invitation-only event has previously attracted a price tag of $10,000-a-head for millionaires and businessman to attend when Malcolm Turnbull was PM.

Take a tour of Justin Hemmes' historic waterfront mansion – Vogue Living http://t.co/zGB0CIBjEc pic.twitter.com/ApDnXtw7IJ

— Vogue Living (@VogueLiving) June 23, 2015

But unions claim the Merivale empire got rich by ripping off workers.

“We see today Liberals would rather rub shoulders with billionaires who rip off their workers than stand up for the rights of workers to be paid the penalty rates they should receive,” United Voice’s Jo-anne Schofield said.

“This is the same Justin Hemmes, who just this year was exposed paying 3000 staff thousands of dollars less than they would be entitled to under the current award.”

The New Daily has contacted Mr Hemmes’ Merivale empire for comment.

In January, the Fair Work Commission terminated the agreement after the union argued it allowed Merivale to underpay staff below the industry award.

Unions described it as a “zombie agreement” because it was out of step with modern awards and they claimed did not penalty rates for weekends.

After the agreement was terminated, Merivale was accused of having a “bizarre whinge” about paying staff their entitlements to the Fair Work Commission.

“Merivale will need to consider the viability of business practices which, while viable under the EBA, may not be viable under the modern award,” human resources manager Kate Tones wrote to Fair Work.

The Merivale group owns a long list of high-profile establishments including Ivy, The Beresford and The Establishment, and the Newport Hotel on the northern beaches.

“The workers had to fight in the Fair Work Commission to kill off Merivale’s “zombie” workplace agreement, which dated back 12 years to the worst excesses of the Howard government’s WorkChoices agreements,” Ms Schofield said.

“One of the brave young applicants was out of pocket $3000 in a year – or missed out on getting an extra 20 per cent of his total salary – because the zombie agreement ruled out penalty rates for evening and weekend work.”

But the Labor leader Bill Shorten is no stranger to rubbing shoulders with billionaires in their mansions.

In fact, the ALP recently flogged $5000-a-head tickets for a fundraiser at billionaire Anthony Pratt’s Kew mansion Raheen.

The Pratt family has a net worth of $12.9 billion. Their links with the Labor leader go back decades after they met through Mr Shorten’s first wife Debbie Beale.

The late Dick Pratt provided his private jet in 2006 to get Mr Shorten back to the Beaconsfield mine disaster when he was leading the Australian Workers’ Union.

His close links prompted a blistering attack from Malcolm Turnbull in Parliament two years ago, when he slammed Mr Shorten as a “simpering sycophant” and a “parasite”.

“There was never a union leader in Melbourne that tucked his knees under more billionaires’ tables than the Leader of the Opposition,” Mr Turnbull said.

“He was such a sycophant, a social-climbing sycophant if there ever was one.”

Mr Turnbull accused Mr Shorten of “knocking back Dick Pratt’s Cristal” and “lapping it up”.

“This sycophant, blowing hard in the House of Representatives, sucking hard in the living rooms of Melbourne, what a hypocrite,” Mr Turnbull said.

“They call themselves the Labor Party; well Mr Speaker, manual labour is a Mexican band as far as they are concerned. Most of them have never done a day’s work in their lives.”