(Bloomberg News) A bipartisan group of U.S. senators urged regulators implementing derivatives measures under the Dodd-Frank Act to move cautiously so the rules can be "completed without unintended consequences."

Treasury Secretary Timothy F. Geithner, Federal Reserve Chairman Ben S. Bernanke and two other top officials were warned against "overly prescriptive rules" that might push market participants abroad in a letter signed by 13 members of the Senate Banking and Agriculture committees and dated yesterday.

"If the major overhaul of our derivatives market is implemented hastily, agency rulemakings could have negative effects on our economy at a time when we can least afford it," the lawmakers said in the letter signed by three Democrats and ten Republicans including Senator Mike Johanns of Nebraska, who serves on both the Banking and Agriculture committees.

The Securities and Exchange Commission and the Commodity Futures Trading Commission are leading efforts to regulate the $583 trillion over-the-counter derivatives market after largely unregulated trades helped fuel the credit crisis. SEC Chairman Mary Schapiro and CFTC Chairman Gary Gensler also were sent copies of the letter.

The lawmakers urged regulators to exempt "end-users"-non-financial firms that use derivatives to hedge business risk-from margin requirements stipulated by Dodd-Frank. Failing to do so would "blatantly disregard" the law's intent, they said.

Swaps and other derivatives are financial instruments whose value is based on an underlying security or benchmark, such as a stock option. Companies may use them to hedge risks and other investors employ them to bet on markets.

The letter was signed by Republican Senators Pat Roberts of Kansas, Thad Cochran of Mississippi, Ron Johnson of Wisconsin, David Vitter of Louisiana, Mike Crapo of Idaho, Kay Bailey Hutchison of Texas, Roger Wicker of Mississippi, John Boozman of Arkansas and Jerry Moran of Kansas as well as Johanns. Democrats Max Baucus of Montana, Herb Kohl of Wisconsin and Jon Tester of Montana also signed the letter.