The IRS is finally ready to make good on threats to strip U.S. passports from Americans who owe more than $52,000 in overdue taxes.

The tax collector and the State Department are escalating enforcement of the Fixing America's Surface Transportation (FAST) Act. This law enables them to deny passport applications or revoke existing passports due to outstanding debts.

The enforcement effort, which began in February 2018 for debts of $51,000 and higher, has thus far covered applications for new or renewed passports. (The higher threshold of $52,000 for 2019 reflects an annual adjustment for inflation, although the IRS could not confirm.)

Now, the IRS will actively begin referring unresolved cases to the State Department for potential revocation, IRS spokeswoman Cecilia Barreda told CNBC.