Washington, D.C. ? Congressional Republicans attached a measure cracking down on Internet gambling to a bill aimed at enhancing port security that passed Saturday.

Senate Majority Leader Bill Frist, R-Tenn., and Sen. Jon Kyl, R-Ariz., pushed for the gambling provision to be added to the larger bill.

Online gambling generally is illegal in most circumstances, but it is something that is difficult to enforce. The new measure tackles that by prohibiting gamblers from using credit cards, checks and electronic fund transfers to settle their online wagers.

The House passed a version of the Internet gambling bill in July, but the Senate has taken no action on similar legislation.

Federal officials have made recent arrests involving offshore companies operating Internet gambling sites. The Internet gambling industry is headquartered almost entirely outside the United States, although many of its customers live in the U.S.