Roger Best, a partner at Clifford Chance, said that since October 2005, when an appeal by the so-called NatWest Three was knocked back, he had received a surge in the number of concerned calls.
"Most businessmen used to think 'well, I behave within the UK law, I'm OK'," he said. "What cases like the NatWest Three have done is make people think not only about UK law but about US law as well.
"Say, for example, you are involved with online gambling [technically an illegal activity in the US]. Are you now at risk of being extradited to the US?"
This sort of unrest across UK business was likely to continue unless the Government intervened, Mr Best said. "US prosecutors have different judges and resources and they will continue to be very tough."
David Bermingham, Gary Mulgrew and Giles Darby - the NatWest Three - lost a lengthy extradition fight to the US last week. The former Greenwich NatWest executives are accused of conspiring to defraud their employers of $7.3m (£3.9m) in an Enron-related deal. They deny any wrongdoing.
They will be flown out to face trial on seven counts of "wire fraud" in Houston, Texas, later this month.
The three have been extradited under the 2003 Extradition Act, which the US government introduced to fight terrorism. However, critics say that instead, it has been used on businessmen.
According to Clifford Chance, 46 extraditions were requested by US between January 2004 and April 2006, 19 related to financial crimes and just three to terrorism.