The FBI has frozen access to Neteller accounts as part of its ongoing investigation into the company.
Neteller provides electronic wallet services which were popular with gambling sites because they allowed US residents to gamble without using credit cards which would give away their home addresses - most gambling sites took this action to try and stop US citizens using their services.
According to USA Today, FBI agent Neil Donovan said the funds were being kept as evidence. He told the paper some customers may get their money back.
An update on the Neteller website warns US members that it can no longer accept their funds or transfer them to gambling sites. The site also says it will no longer accept US residents as new members of Neteller. The company has also stopped peer-to-peer transactions.
US authorities arrested two former executives of the company in January. They were charged not under new US legislation, but for "conspiring to transfer funds with the intent to promote illegal gambling".
The two are due to appear in court 14 February in New York.
The company is based in the Isle of Man and is regulated by the Financial Services Authority. ®