The chairman of UK-listed online gambling company World Gaming, James Grossman, has quit the business.
US authorities are trying to crack down on online gambling
Mr Grossman's move comes as fears grow that top executives at internet gaming firms could be arrested in the US.
The former chairman of Sportingbet and chief executive of Betonsports have both been arrested recently amid allegations of breaking US gaming laws.
World Gaming is listed on London's Alternative Investment Market and operates largely out of Antigua.
A non-executive director at the firm, Clare Roberts, has also resigned.
The Financial Times reports that several online gaming firms have told investors that their executives are avoiding trips to the US for fears they may be arrested.
Mr Grossman is a lawyer who served under former US President George H.W. Bush and was a representative on the United Nations Development Programme, whose work regularly required him to travel to the US.
Earlier this month, the former chairman of online gaming firm Sportingbet, Peter Dicks, was allowed to return to the UK by a New York court, but he must return for a further hearing on 28 September.
Mr Dicks was held under a warrant issued by state authorities in Louisiana accusing him of "gambling by computer".
In July, Betonsports' chief David Carruthers was arrested on racketeering charges at Dallas airport.
Online gaming is a $12bn-a-year business in the US that is expanding despite the government's opinion that it violates a law against placing interstate bets using telephone lines.
This has prompted Congress to propose a US law banning banks and credit card companies from processing internet gambling payments.