Country that "doesn't recognize" US citizenship?

[lpntw]

My question is about how some countries who "don't recognize" dual citizenship react if their citizens gain U.S. citizenship.

My husband is a Mongolian citizen. He has a U.S. green card and has been in the U.S. for over six years. He wants to get U.S. citizenship and retain Mongolian citizenship. Mongolian law is says that "involuntary loss of citizenship" is impossible, and also that dual citizenship is "not recognized." It doesn't say getting another citizenship is illegal, or will be punished, or will result in losing Mongolian citizenship. I know that a number of countries "do not recognize" dual citizenship, but people still use their passports from these countries after becoming U.S. citizens.

The USCIS does not require him to actually go to the Mongolian consulate and have his Mongolian citizenship annulled. But let's say he gets US citizenship and keeps his Mongolian passport. When he flies to Mongolia from the U.S., he will have to exit using his U.S. passport. Then can he still show his Mongolian passport (with no U.S. exit stamp) to enter Mongolia, or will that cause problems? What happens if Mongolian officials find out that he has a U.S. passport and never renounced Mongolian citizenship? Do they just "not recognize" it and leave it at that, or are there consequences?

Also, what happens when he needs to renew his Mongolian passport in the U.S.? Does that become out of the question?

This is a hard question, so thank you in advance for any information, guesses, experiences that you can share–not just about Mongolia, but other countries with this kind of policy, too.

[reabs]

Probably the best source on what the options and consequences are would be the Mongolian consulate.

Until recently, the country I'm originally from did not permit dual nationality. A friend of mine tried what you described - exit with one passport and attempt entry with another without an exit stamp. The ECO at the destination airport queried why the passport (A) bore no entry/exit stamps and my friend confessed to having another passport (B). ECO asked for it saying he needed to stamp the passport (B) he used to leave the foreign country. After stamping it, he returned it (B), issued him with a receipt for the other passport (A), advised him it along with his citizenship had been forfeit the minute he got foreign citizenship before waving him off with a smile.