At first blush, ACTU secretary Sally McManus and one of Wall Street's most powerful bankers, Jamie Dimon, would seem unlikely allies on the key battlefield of industrial relations and pay.

Key points: In Australia, 700,000 workers face pay cuts for Sunday shifts under Fair Work Commission ruling

In Australia, 700,000 workers face pay cuts for Sunday shifts under Fair Work Commission ruling ACTU chief Sally McManus has found an unlikely ally in US banking chief Jamie Dimon

ACTU chief Sally McManus has found an unlikely ally in US banking chief Jamie Dimon Dimon, chief executive at JPMorgan, says raising wages for lower-paid workers helps small business

In her so far short tenure leading Australia's trade unions, Ms McManus has made it clear she has little time for neo-liberal, market-focused economics and trickle-down wealth creation.

Mr Dimon, on the other hand, is a billionaire and has run the investment bank JPMorgan since well before the GFC struck.

JPMorgan is one of the "big four" US banks with a market capitalisation of $400 billion.

Mr Dimon's stake in the bank is currently valued at around $US530 million ($700 million) and rising on the so-called "Trump trade" which includes plans for an aggressive deregulation of the big banks in the US.

His sphere of influence extends from the Democratic Party through to the Trump administration, where he is said to have the ear of the President.

He also firmly believes cutting pay and conditions for workers is not a brilliant idea.

Low-paid workers facing cuts for Sunday work

For Ms McManus, Mr Dimon is a powerful, if unwitting, ally to have as she prepares to lead the fight against cuts to Sunday penalty rates in the retail and hospitality sectors.

About 700,000 workers are facing a reduction in pay for Sunday shifts after the Fair Work Commission agreed with employers that the current penalty rates were too high.

It remains an open question as to whether the new jobs that have been promised in shops and fast food outlets materialise, or if owners will put their workers' pay cuts straight into their own pockets.

Ms McManus has put business on notice that unions under her watch will be vigorous in fighting for what they believe are their rights.

"I believe in the rule of law where the law is fair, when the law is right. But when it's unjust, I don't think there's a problem with breaking it," she famously told the ABC's 7.30 program.

As for the wages of those at the bottom, the JPMorgan boss has come out strongly on the side of the workers.

"I tell the people at JPMorgan I'm more worried about the pay of our lower-paid people than our higher-paid people," Mr Dimon said in an interview with Bloomberg Business Week.

And he knows a thing or two about pay.

His $35-million-a-year salary makes Australia's highest-paid banker, CBA's Ian Narev, look like a middle-ranking teller at a suburban branch.

And like Australia's banks, JPMorgan has a sales-driven culture that saw its financial market traders, on enormous salaries, play a key role in delivering the global financial crisis.

Unlike Australia's banks with their financial planning scandals, though, JPMorgan has paid a heavy price for its bad behaviour.

About $30 billion in fines, at last count.

It says a lot about the dominance of the world's big banks that JPMorgan can pay so much — and it is not alone — and hardly miss a beat.

Lower wages can mean higher costs

But on the issue of pay, Mr Dimon believes attacking those at the bottom is not good for business.

Mr Dimon was speaking in the context of the United States, where just like Australia's Sunday penalty rates, there has been a rancorous debate around the minimum wage.

In the US the minimum wage currently stands at $10 an hour, while in Australia it is $17 an hour.

As is the case here with penalty rates, the debate in the US has polarised on predictable lines, with many employers and Republican politicians on one side, and workers and Democrats on the other.

"If your business can afford it, raise the minimum wage," said Mr Dimon, a big employer breaking ranks and siding with the workers.

"Raising wages at the bottom will help small business.

"You'll attract better people, they'll be paid more, you'll probably have less attrition."

It's a view echoed in Australia by the ACTU's Ms McManus.

"Workers will back businesses that look after them," she told the ABC's 7.30.

As employers in many Australian businesses mull over their new-found ability to cut the wages of those at the bottom, a big issue they'll need to resolve is whether the money saved will be greater than the cost to the business from having a disenfranchised workforce.

Mr Dimon thinks the answer is no.