Important Note: I am not a lawyer and the following is my ad-hoc interpretation of data. Do not consider the following to be a legal description of your situation.

When I wrote about US Renunciations Hitting New Record, Eric from notlearningcantonese wrote:

And not to sound like a tin-foil-hatter, but I've personally come to the conclusion that renunciation statistics are deliberately being under-reported. I didn't believe this theory at first because the one renunciant I know personally (a classmate) actually did show up in the list, but every time I dig into the numbers I find something suspicious. E.g. there's about 8,000 Americans per year naturalising in EU countries, according to Eurostat --- but the number who naturalise in countries which disallow dual citizenship is greater than the number of names in the "name and shame" list.

And that got me to digging. What I needed, specifically, was source data. First, I grabbed the list of Americans who have acquired EU citizenship. Their interface is an abomination, but once you've assembled the correct data, you can export it in a variety of formats.

Then I marked the countries which do not appear to allow multiple citizenships and I summed the total number of Americans acquiring citizenships in those countries, per year, discarding years before 2002 as the data seemed too incomplete.

Then I added in the Federal Register data on individuals who have chosen to expatriate. Actually, this data is so abysmally organized that I calculated 2002 and 2003 and grabbed the remaining years from the International Tax Blog.

As for the countries in the EU which do not allow dual citizenship, they are, as near as I can tell:

• Austria
• The Czech Republic
• Germany
• Latvia
• Lithuania
• Luxembourg
• Netherlands
• Slovakia
• Slovenia
• Spain

Of course, it should be noted that there are always exceptions to the rule. For example, the Netherlands generally will not allow a naturalized citizen to hold another citizenship, unless they are naturalized via marriage. All countries have all sorts of exceptions, but I suspect you'd find that the majority of naturalized citizens do not fall under the exceptions.

Further, you'll note that the data below is incomplete. Not all countries reported their figures for the Eurostat data, with the UK's omission being particularly glaring for 2009. (Dashes indicate missing data).

Update: Apparently, Denmark's figures should have been included. My check of countries which forbid dual citizenship was pretty quick, so I'm not surprised. Enough American become Danish every year to definitely increase the number of effective renunciations.

Section 349 of the Immigration and Nationality Act (8 U.S.C. 1481), as amended, states that U.S. citizens are subject to loss of citizenship if they perform certain specified acts voluntarily and with the intention to relinquish U.S. citizenship.

I think it could be reasonably argued that voluntarily acquiring citizenship in a country which requires that you relinquish your US citizenship falls under Section 349 of the Immigration and Nationality Act. Or you might claim not that you lost your US citizenship, but that you assumed you lost it since that is the law of your new country, thus making a plausible defense for why you should not be subject to US taxes.

Further, when you check the number, realize that US expats in Europe are only about one quarter of worldwide US expats.

One missing piece of information: I have not been able to find out the process by which people demonstrate to their new country that they have given up their previous citizenship. I've done a lot of searching on the Web and posted questions to message boards, but I have no answers yet.

The Federal Register data on US renunciations are of very bad quality and the collection processes are abysmal, so it's difficult to get real numbers here. Further, I've read (and don't have links for) that both Mexico and Japan don't actually force you to relinquish your citizenship, even though it's required by law.

However, if you're an expat whose acquired citizenship in one of these countries and you're in FATCA hell with the IRS trying to drive you into bankruptcy, this could make for a very interesting defense: even if you don't formally renounce, you may argue that you lost your citizenship anyway. I've never heard of a case where someone has argued this defense before, but it would be very, very interesting.

Why are reported renunciations so low? Because to show up in Federal Register list, you have to formally renounce with the US State Department and they turn that information over to the IRS, who then publishes that information in the Federal Register. This appears to be a manual process, with many names omitted and sometimes duplicated. Further, if you lose your citizenship outside of this process, it is presumably not reported.

While it appears that the number of Americans acquiring EU citizenship has remained fairly constant over the past decade, with 1,781 (most of them likely in Canada due to FATCA issues) Americans being reported as renouncing last year (the highest on record) and the probability that this number (whether real or reported) is likely to be even higher next year, I think there's a chance that the number of ex-Americans might start to approach levels that policy makers sit up and take notice — particularly if anyone argues successfully that they lost their US citizenship due to acquiring an exclusive foreign citizenship.

http://overseas-exile.blogspot.fr/2012/03/more-americans-giving-up-citizenship.html