The number of Americans renouncing U.S. citizenship declined 13 percent in the final half year before rules that make it harder to hide assets from tax authorities came into force.

People giving up their nationality at U.S. embassies fell to 1,577 in the six months through June, from 1,809 in the year- earlier period, according to Federal Register data published today.

Tougher asset-disclosure rules effective as of July 1 under the Foreign Account Tax Compliance Act, or Fatca, prompted 576 of the estimated 6 million Americans living overseas to give up their passports in the second quarter. The appeal of U.S. citizenship for expatriates faded as more than 100 Swiss banks turn over data on American clients to avoid prosecution for helping tax evaders.

“Fatca and the Swiss bank disclosure program has intensified the search for U.S. nationals beyond all measure,” said Matthew Ledvina, a U.S. tax lawyer at Anaford AG in Zurich. “It’s shocking the levels of due diligence they are going through to ensure they have cleaned house.”

Swiss banks are trawling through records going back to the 1990s to find clients with U.S. addresses and telephone numbers, and those who received schooling in the country, Ledvina said. Those identified as U.S. persons are either being asked to leave or placed in special U.S.-only sections of the institution, he said.

Imposing Tax

The U.S., the only Organization for Economic Cooperation and Development nation that taxes citizens wherever they reside, stepped up the search for tax dodgers after UBS AG paid a $780 million penalty in 2009 and handed over data on about 4,700 accounts. Shunned by Swiss and German banks and with Fatca looming, almost 9,000 Americans living overseas gave up their passports over the past five years.

Fatca requires U.S. financial institutions to impose a 30 percent withholding tax on payments made to foreign banks that don’t agree to identify and provide information on U.S. account holders. It allows the U.S. to scoop up data from more than 77,000 institutions and 80 governments about its citizens’ overseas financial activities.

In establishing the 2010 Fatca law, Congress and President Barack Obama in effect threatened to cut off banks and other companies from easy access to the U.S. market if they didn’t pass along such information. It was projected to generate $8.7 billion over 10 years, according to the congressional Joint Committee on Taxation.

Voluntary Disclosures