Democratic presidential candidate Hillary Clinton proposed a 4 percent tax on people making more than $5 million per year on Monday, a plan she said she would impose were she elected. Speaking at an organizing event in Iowa, Clinton called the tax a "fair share surcharge" which she said would ensure that the top 0.02 percent of the taxpaying public pay higher tax rates.

"I want to go further and impose what I call a fair share surcharge on multi-millionaires because right now, we're behind and we need to get the wealthy and the corporations to pay for their fair share, so I can keep my promise, which is I will not raise taxes on the middle class," said Clinton, according to Reuters.

A Clinton campaign aide elaborated, saying the surcharge would generate $150 billion over the next decade and ensure effective rates rise for tax payers who are avoiding a tax payment that's equal.

"This surcharge is a direct way to ensure that effective rates rise for taxpayers who are avoiding paying their fair share, and that the richest Americans pay an effective rate higher than middle-class families," said the aide, according to The Hill.

The proposal builds off the principle of the "Buffett Rule," named after billionaire investor Warren Buffett, who campaigned with Clinton last month. Buffett has criticized tax policies that allow the rich to pay lower rates than the middle class and under the proposed measure, a minimum tax rate of 30 percent would be imposed on individuals making $1 million or more annually.

This "fair share surcharge" adds to a list of other proposals Clinton has detailed during her campaign, reported the AFP. Others include a $350 billion plan to reduce debt for college students, a $275 billion plan to invest in infrastructure and a $30 billion plan to assist coal-dependent regions.

Clinton is expected to unveil more elements to her proposal later this week.