SAN FRANCISCO (MarketWatch) — Lawmakers looking to bolster the nation’s finances may want to consider withholding U.S. passports from people with unpaid tax bills. Doing so might have netted almost $6 billion in 2008 alone, according to a report made public by the U.S. Government Accountability Office on Monday.

About 1% or 224,000 of the 16 million passports issued in fiscal year 2008 went to people who owed more than a total of $5.8 billion on their taxes. And that’s counting only taxpayers who reported what they owed or those whom the IRS caught through an audit. The figure doesn’t include people who never filed a tax return or who understated what they owed, according to the GAO report.

Some taxpayers who received passports that year “accumulated substantial wealth and assets, including million-dollar houses and luxury vehicles, while failing to pay their federal taxes,” according to the GAO, which conducted the study of U.S. State Department, IRS and other data at the behest of the U.S. Senate Finance Committee. Read the report on the GAO site.

One passport recipient is a World Bank employee who owes $300,000 to the IRS. Another is a gambler who owes $46.6 million in unpaid taxes and who “gambled tens of millions of dollars at the same time the income taxes were not paid,” according to the report.

“One passport recipient purchased a house for about $2 million and investment property for about $1.5 million while the recipient owed over $1 million in federal taxes,” the GAO report said. Two people secured passports in the names of dead people, according to the report.

The investigation focused on 25 cases; they are not necessarily representative of all instances in which a tax debtor received a passport. “These are some of the more egregious,” said Greg Kutz, director of the GAO’s forensic audits and investigative service and the report’s author.

Currently, the U.S. State Department, which doles out passports, is not authorized to withhold passports to people who have unpaid tax bills, and the IRS can’t disclose taxpayer information to the State Department unless the taxpayer allows it.

But the State Department does have authority to withhold passports from people who owe more than $2,500 in child support. That program has collected about $200 million in child-custody payments since 1998, the GAO said.

“If Congress is interested in pursuing a policy of linking federal tax-debt collection to passport issuance, it may consider taking steps to enable [the State Department] to screen and prevent individuals who owe federal taxes from receiving passports,” the GAO report said.

But will lawmakers make the change? That’s hard to say.

“I don’t know if it’s likely to happen. We recommend Congress consider this as a viable option policy-wise,” Kutz said.

The State Department “has done it before with respect to child-support payments,” he said. “You have to implement in a way that protects privacy … but this has been done before so it’s not like recreating the wheel.”