The US House of Representatives has backed a bill which aims to rein in online gambling.
US lawmakers say 2,300 gambling sites now exist online
The bill aims to limit internet gaming by making it illegal for US-based banks and credit card firms to make payments to online gambling sites.
Estimates suggest the online gaming industry generates $12bn (£6.4bn) a year worldwide, half from US gamblers.
As yet it is unclear whether the US Senate will make the bill law ahead of elections in November.
Critics have attacked the proposals as an "outrageous" measure, claiming it aims to stir up the more conservative sectors of society ahead of the elections - and so boost the Republican party's chances.
However, one of the bill's sponsors, Republican Bob Goodlatte, claimed the plans aimed to control a "scourge on society" which causes "innumerable problems".
The US plans have come under close scrutiny from some UK-listed sites such as Partygaming and 888 Holdings - owners of 888.com - amid concerns that earnings will suffer if the US government does clamp down on online gaming.
Gambling is illegal in many parts of the US, but internet gaming firms like 888 have millions of US customers, because they are based offshore in countries that allow gambling and are out of reach of US laws.
The bill would make it illegal to accept payments from people who live where federal or state law prohibits betting.