A group of wealthy Americans are pleading for US presidential candidates to tax them and their ultra-rich peers more if they are elected.

Key points: The group wants the United States' richest citizens, including themselves, to pay a wealth tax

The group wants the United States' richest citizens, including themselves, to pay a wealth tax Money raised from these taxes could be used to combat climate change and improve the US health system, they say

Money raised from these taxes could be used to combat climate change and improve the US health system, they say They says the US has a moral responsibility to tax the rich

Dubbed the Billionaire's Club by US media, the group's members include Facebook's co-founder and a Disney heiress, who say paying higher taxes is their "patriotic duty".

They penned a joint letter urging presidential candidates to back a wealth tax for the richest of America's rich.

"Support a moderate wealth tax on the fortunes of the richest one-tenth of the richest 1 per cent of Americans — on us", they wrote.

"America has a moral, ethical and economic responsibility to tax our wealth more.

"A wealth tax could help address the climate crisis, improve the economy, improve health outcomes, fairly create opportunity, and strengthen our democratic freedoms.

"Instituting a wealth tax is in the interest of our republic."

Those who signed the letter were Louise J. Bowditch, Robert S. Bowditch, Abigail Disney, Sean Eldridge, Stephen R. English, Agnes Gund, Catherine Gund, Nick Hanauer, Arnold Hiatt, Chris Hughes, Molly Munger, Regan Pritzker, Justin Rosenstein, Stephen M. Silberstein, Ian T. Simmons, Liesel Pritzker Simmons, Alexander Soros and George Soros.

At least one other wealthy activist signed off as "Anonymous".

"I try to be a thoughtful investor and philanthropist, but neither of these is a substitute for good public policy. That's why I'm signing this Open Letter," Ms Pritzker Simmons said on Twitter.

Warren's 'Ultra-Millionaire' singled out

The group said they did not write the letter as an endorsement of a political candidate, however, they pointed out Democrats Elizabeth Warren, Pete Buttigieg, Beto O'Rourke and Tim Ryan were supportive of the idea.

They went into detail about Ms Warren's proposed Ultra-Millionaire Tax, which would target the 75,000 richest families in the US. It is estimated it would generate nearly $US3 trillion ($4.3 trillion) in a decade.

That policy would only affect those worth $US50 million or more.

Ms Warren re-tweeted a link to a New York Times story about the letter, saying her policy would "give every family a shot at the American dream".

Ms Warren wants an extra tax on those worth $US50 million or more. ( Reuters: Yuri Gripas )

According to a February report from the Washington Post, 61 per cent of respondents in a US poll backed the idea of a wealth tax, with the article suggesting the policy was a rising trend among US voters.

An earlier poll from Fox News found 70 per cent of participants backed the idea of increasing taxes on families that earned more than $10 million annually.

Of the Republican voters in the Fox poll, 54 per cent were in favour of higher taxes for the wealthy.

Trump once spruiked a wealth tax

Now-US President Donald Trump proposed a one-off wealth tax to pay off the United States's national debt back in 1999.

The tax would target individuals and trusts worth $US10 million or more at a rate of 14.25 per cent.

At the time, his plan was predicted to raise $US5.7 trillion.

"By my calculations, 1 per cent of Americans, who control 90 per cent of the wealth in this country, would be affected by my plan," Mr Trump said in a statement to CNN in 1999.

"The other 99 per cent of the people would get deep reductions in their federal income taxes.

"It is a win-win for the American people, an idea no conventional politician would have the guts to put forward."

In 1999 Mr Trump proposed imposing a one-off wealth tax. ( AP: Susan Walsh )

How big is the wage gap in the US?

According to the Washington Centre for Equitable Growth, the richest 1 per cent of America's households control about 40 per cent of the nation's wealth.

An analysis of US Federal Reserve figures from the People's Policy Project found the country's richest 1 per cent got about $21 trillion richer between 1989 and 2018.

In that same period of time, the bottom 50 per cent got about $US900 billion poorer.

The group behind the letter cited data projections that the richest 0.1 per cent of Americans would pay 3.2 per cent of their wealth in taxes.

The same data projected the bottom 99 per cent of households would pay a higher percentage of 7.2 per cent.

"[Billionaire investor] Warren Buffett has pointed out that he is taxed at a lower rate than his secretary," the group wrote.

"Taxing extraordinary wealth should be a greater priority than taxing hard work.

"The most fortunate should contribute more."