Democratic presidential candidate Hillary ClintonHillary Rodham ClintonFive big Trump narratives to watch NBC: Russia setting up dossier on Trump Chelsea Clinton attends Muslim solidarity rally in NYC MORE on Monday called for an additional 4 percent tax on people making more than $5 million per year.
Clinton called the tax a “fair share surcharge” that would make sure wealthier taxpayers pay higher tax rates.
The surcharge, which Clinton unveiled at an organizing event in Iowa Monday afternoon, would raise more than $150 billion over 10 years, the aide said, and is part of Clinton's plan to build on the principle of the "Buffett Rule" to raise the effective tax rates of the rich.
The Buffett Rule, named after philanthropist billionaire Warren Buffett, would ensure that those making more than $1 million pay at least 30 percent of their incomes in taxes.
Clinton intends to release more proposals that would increase the amount of taxes paid by the wealthy later this week, the aide said.
The former secretary of State also plans to release more proposals that would provide tax relief to the middle class. She has already proposed tax credits for excessive healthcare costs and for family members caring for ailing parents and grandparents.
The campaign of Sen. Bernie Sanders (I-Vt.), Clinton's main rival for the Democratic presidential nomination, criticized the proposal. Sanders spokesman Michael Briggs called the proposal "too little too late."