Here is a sign that life is getting complicated for U.S. taxpayers with assets abroad: More of them are deciding they are better off cutting official ties with America.

In the first half of 2013, 1,809 people renounced their American citizenship or permanent-resident status, according to a tally by Andrew Mitchel, a tax lawyer who tracks U.S. data. At that pace, the 2013 total would double the previous high of 1,781 renunciations in 2011.

Daniel Kuettel, a Colorado native who lives near Zurich, says he gave up his U.S. citizenship in October because he feared he wouldn't be able to get a mortgage now that some Swiss banks are cutting ties with American clients.

"It was a really difficult decision. I had to think about what was best for me and my family, to reduce the risk," says Mr. Kuettel, a 41-year-old software developer. He says his income was below the limit the U.S. allows overseas taxpayers to exempt and he owed no U.S. taxes.

The increase in renunciations is one sign that ordinary Americans who have lived and worked abroad for years, as well as green-card holders in the U.S. and overseas, believe they are at growing risk because of the intensifying government pursuit of undeclared foreign assets.