Federal Reserve spokeswoman Susan Stawick declined comment.

The letters follow an April 2 House hearing where representatives of the financial agencies said they were struggling to write regulations to carry out the gaming restrictions Congress passed in 2006.

Louise Roseman, director of bank operations and payment systems for the Federal Reserve, testified an Internet gambling ban cannot be "ironclad."

Roseman and Valerie Abend, a deputy assistant secretary for the Treasury Department, agreed the 2006 legislation does not define "unlawful Internet gambling."

After that hearing, Frank and Paul introduced a bill to prevent the Federal Reserve and Treasury Department from going forward with regulations to implement the Internet gambling ban.

In their letters this week the lawmakers served notice that they intended to "vigorously pursue" legislation to shelve the rules, thus blocking the Internet gambling ban from taking full effect.

Frank also introduced a bill last year to scrap the ban and require the Department of Treasury to regulate Internet gambling in the United States.

Another sign that opposition may be growing came Tuesday with the announcement by the Poker Players Alliance, a lobbying group seeking an exemption from the ban, that its membership has reached 1 million.

Rep. Dean Heller, R-Nev., who is a member of the financial services committee, said in a statement he is "not yet convinced that the rulemaking process should be dropped altogether at this point."

Rep. Jon Porter, R-Nev., said the letters underscored the need for a federal study of Internet gambling.

"The point is the (Bush) administration and Congress do not have a road map to make the regulations," Porter said.

Heller and Porter are co-sponsoring a bill by Rep. Shelley Berkley, D-Nev., to appoint the National Research Council of the National Academy of Sciences to study Internet gambling for one year.

"Those pushing these regulations in the face of strong opposition are more concerned with scoring political points than they are about protecting the rights of adults in the U.S. or the actual cost of implementing this truly Byzantine law," Berkley said in a statement.