An annual 2% levy on fortunes exceeding $1 billion is the starting point for a global proposal to increase the burden on undertaxed billionaires, French economist Gabriel Zucman said on Tuesday.

Zucman, who founded the independent EU Tax Observatory, was commissioned by the Brazilian G20 presidency to present a report on the issue for discussion by the finance ministers of the world's 20 largest economies at a meeting in July.

"The goal of this blueprint is to offer a basis for political discussions — to start a conversation, not to end it," he wrote in the report released on Tuesday. "It is for citizens to decide, through democratic deliberation and the vote, how taxation should be carried out."

Zucman, a professor at the Paris School of Economics and the University of California, Berkeley, stressed that enhanced transparency on company ownership would aid tax authorities in its potential implementation.

According to the economist, implementing the rule would raise $200 billion to $250 billion annually in tax revenue from about 3,000 individuals.

Extending the tax to those with over $100 million would generate an additional $100 billion to $140 billion, he said.

(Reporting by Marcela Ayres; Editing by Gabriel Araujo and Franklin Paul)