My understanding is that this is not correct. The US does have strong AntiCorruption Laws that deal with US entities operating overseas.

Transparency International have good references. http://www.transparency-usa.org/links/index.html

A quick search found this signed by Brazil and US in 1996.

B-58: INTER-AMERICAN CONVENTION AGAINST CORRUPTION

'(3) TRANSNATIONAL BRIBERY.--Current United States law provides criminal sanctions for transnational bribery. Therefore,it is the understanding of the United States of America that no additional legislation is needed for the United States to comply with the obligation imposed in article VIII of the Convention.'

http://www.oas.org/juridico/english/Sigs/b-58.html