Merchants such as Target Corp. [s] and Walmart Inc. /zigman2/quotes/207374728/composite WMT -0.35% signed on to a letter asking Congress to pass a law that would require options for the routing of credit-card transactions over alternative networks, according to The Wall Street Journal . Sen. Dick Durbin, an Illinois Democrat, and Sen. Roger Marshall, a Kansas Republican, who introduced such a bill back in July, said that alternate routing options would increase competition and lead to lower swipe fees when people use many Visa Inc. /zigman2/quotes/203660239/composite V -1.04% and Mastercard Inc. /zigman2/quotes/207581792/composite MA -0.42% credit cards. "Swipe fees for credit cards are higher in the United States than anywhere else in the industrialized world-more than seven times as high as Europe," a group of more than 1,600 merchants said in their letter, the Journal reported Wednesday. Debit cards already carry a requirement for routing options in most cases. Visa Chief Financial Officer Vasant Prabhu addressed the proposed legislation at a Goldman Sachs conference earlier this week, saying that there is already "a ton of competition" in the credit-card business and that reductions in interchange fees as a result of any new laws could impact the rewards landscape for consumers.