Did you know the U.S. Government will be able to deny new, or revoke current, passports of people with serious tax debts?

Congress is poised to enact a law denying or revoking passports for U.S. citizens who haven’t paid their taxes.

Under a new law expected to take effect in January, the State Department will block Americans with “seriously delinquent” tax debt from receiving new passports and will be allowed to rescind existing passports of people who fall into that category. The list of affected taxpayers will be compiled by the Internal Revenue Service using a threshold of $50,000 of unpaid federal taxes, including penalties and interest, which would be adjusted for inflation.

The rule has been passed in similar versions by both the House of Representatives and the Senate. It is part of a highway-funding bill, H.R. 22, that is before a conference committee. Congress is expected to pass it in early December.

In most cases, the passport provision would apply if a taxpayer is subject to a lien, which advises creditors of a debt to the IRS, or a levy, which gives the IRS the authority to seize assets. It wouldn’t apply if a taxpayer is in the process of resolving tax debt with the IRS, such as by paying it on an installment plan, or if the taxpayer is contesting the collection either administratively or in court, said David Kautter, a partner at the accounting firm RSM in Washington.

However, the State Department could issue a passport in an emergency or for “humanitarian reasons.” Neither the State Department or Treasury Department would comment while the legislation is pending.

If enacted in current form, the law would take effect on Jan. 1 and would apply to existing tax debts. According to estimates by the Joint Committee on Taxation, the measure is expected to raise $398 million over 10 years.

“If this bill becomes law, it will be imperative for Americans traveling abroad or living abroad to pay attention to IRS notices—assuming they receive them,” said Mr. Kautter.

It’s unclear how many people would be affected. The provision’s most vocal critics are advocates for the some 7 million U.S. citizens living overseas, who need their passports for many purposes, including for work visas or residency permits, and who may not be receiving mail from the IRS.

“Americans abroad need their passports for many routine activities of daily life, such as banking, registering in a hotel, or registering a child for school, and mistakes could be disastrous,” said Charles Bruce, an American lawyer with Bonnard Lawson in Lausanne, Switzerland, who advises American Citizens Abroad, an expatriate group.

Mr. Bruce noted that a report issued in September by the Treasury Inspector General for Tax Administration, or Tigta, a watchdog agency, found that the IRS sent 855,000 notices to U.S. citizens abroad in 2014. According to the report, “IRS data systems aren’t designed to accommodate the different styles of international addresses, which can cause notices to be undeliverable.”

The Tigta report said that “current IRS processes for addressing international mail issues are ineffective or nonexistent.” In response, the IRS said that Tigta’s recommendations wouldn’t overcome the agency’s “budgetary, statutory, and operational constraints.”