Hello and thank you for using Just Answer.
Will they "flag" you? I really do not know their proceedure as entering the country falls under homeland security but I can advise that they do not have to wait for a citizen to come back to get the debt.
A few tax treaties, however, have mutual-collection-assistance provisions that provide the U.S. government witha mechanism for enforcing a judgment for unpaid taxes. For example, treaties with Denmark (Art. XVIII, para. 1), France (Art. 27, para. 1), the Netherlands (Art. XXII, para. 1), and Sweden (Art. XVII) have mutual assistance provisions for collection. The treaties generally provide that either party to the treaty will collect a "finally determined tax" owed to the first country as if it were a tax owed in the second country.
The treaty provisions usually provide that a "requesting state" can ask the other treaty partner to collect a tax as if it were owed in that country.
so if you have money in a bank account in sweden the IRS has the authority to take it away from you?
They can ask the Swedish government to collect the tax from a person in Sweden if the US is owed the tax.