New York (CNN Business) More than a dozen of the richest Americans have a message for 2020 presidential candidates: Tax us more.

In a letter sent to candidates Monday, 18 members of some of the nation's wealthiest families advocated for a wealth tax on people who amassed great personal fortunes, including themselves.

"We are writing to call on all candidates for president, whether they are Republicans or Democrats, to support a moderate wealth tax on the fortunes of the richest one-tenth of the richest 1% of Americans -- on us," said the letter, which was first published in the New York Times Monday.

It said that millions of middle-class Americans already pay a wealth tax annually on their primary form of wealth: property taxes on their homes. The letter points out that Democratic candidates Elizabeth Warren , Beto O'Rourke and Pete Buttigieg have proposed a wealth tax. But the letter's writers said, "Some ideas are too important for America to be part of only a few candidates' platforms."

Berkshire Hathaway BRKA This letter is not the first time that wealthy Americans have called for more taxes on themselves and others who are well-off.CEO Warren Buffett famously said he believed it was wrong that his income was taxed at a lower rate than that of his secretary. That prompted President Barack Obama to propose a minimum tax on millionaires' incomes that became known as the " Buffett rule ." But that and other tax-the-rich proposals have typically been limited to taxes on income or inheritances, not on overall wealth.

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