The bill, sponsored by Representative James Leach, an Iowa Republican, would make it unlawful for credit-card companies to collect payments for transactions with online-gaming sites.

"We expect that it probably will pass the House, and then it will get it sent over probably to the Senate Judiciary Committee," said Holly Thomsen, a spokeswoman for the American Gaming Association, which represents U.S. casino companies.

"When it will run its course through committee and get to the full Senate for a vote is unclear," Thomsen said.

Gambling on the Internet is a $12 billion-a-year business that is growing rapidly offshore. Internet-based casinos such as PartyGaming Plc and 888 Holdings Plc, operating in locations such as Gibraltar and Antigua, rake in billions from U.S. gamblers. MGM Mirage and Harrah's Entertainment Inc. among others are lobbying Congress to study whether online gaming should be legalized in the U.S.

Leach's bill may be combined with one sponsored by Representative Bob Goodlatte, a Virginia Republican, that would force U.S. banks to cooperate with federal law enforcement authorities in shutting down illegal gambling sites.

Goodlatte's measure would make it explicit under U.S. law that gambling over the Internet is illegal. The bill leaves in place an exemption for U.S. horseracing, a provision that has drawn protests from dog track and jai alai interests.

The House Judiciary Committee approved the Leach and Goodlatte bills May 25. The Bush administration supports the legislation and has been prosecuting offshore gaming sites under a 1961 law against using telephone lines to place interstate bets.

In 2005, commercial and Indian tribe casinos and horse- betting operations took in more than $52 billion in gross revenue nationwide, according to a Pew Research Center study citing industry estimates.