Facebook co-founder Eduardo Saverin could be banned from ever returning to the U.S. if Senate Democrats' bill passes

— -- Senate Democrats on Thursday unveiled a bill to punish Americans who renounce their citizenship for tax purposes, pointing specifically to Facebook co-founder Eduardo Saverin, who last fall withdrew his citizenship before the company's billion-dollar initial public offering.

Saverin could save $67 million in tax costs after the Facebook IPO deal by dissociating himself from the United States, and the bill's sponsors say they want to ensure that money ends up in the U.S. Treasury.

Democratic Sens. Bob Casey of Pennsylvania and Charles Schumer of New York outlined the bill Thursday, which would impose a 30 percent capital gains tax on investments within the country on anyone who renounces citizenship to avoid taxes. The bill would also ban Saverin—and others who take similar action—from ever setting foot on American soil again.

"Eduardo Saverin wants to de-friend the United States of America," Schumer said. "Senator Casey and I have a status update for him: Pay your taxes in full or don't ever try to visit the U.S. again."

Saverin currently lives in Singapore, which has no capital gains tax.

Schumer estimated the bill would apply to about 3,000 people.

"This is a small, narrow group," he said. "And they deserve to get the treatment we're giving them."