When an unusual trade advisory crossed his desk last summer, Clemente Vazquez-Bello, a Miami lawyer, sat up straight. After reading the Treasury Department advisory on money laundering through trade channels, Vazquez-Bello had a gut feeling that this would be the year in which the U.S. government would attack the “secondary” currency market — also known as the gray or black market.

The June 1999 advisory was the second warning the government had issued in less than two years.