US call for credit card bill of rights US lawmakers have urged some of America's largest financial companies to "clean up" their credit card practices, amid an ongoing congressional probe of charges and fees imposed on consumers. Senate subcommittee on investigations chairman Carl Levin said few Americans were aware of how the industry's complex credit-rating system can harm their financial health. Executives from Bank of America, Discover Financial Services and Capital One appeared before Congress to explain their practices, as Democratic presidential hopeful and Senator Barack Obama called for a "credit card bill of rights." Lawmakers also heard testimony from Americans battling to pay off their credit card debts who voiced frustration at surprise interest rate hikes and intimidating bank representatives. Janet Hard, a nurse from Michigan, said she was struggling to pay her credit card bills and felt like she was being "robbed" by Discover. The hearing occurred amid the pre-Christmas shopping season when millions of Americans will use credit cards to purchase gifts. US credit card debt has soared in recent years to $US877.1 billion ($1 trillion) in 2006, up over $US100 billion from $US770.5 billion in 2003, according to the Federal Reserve. I'm happy to report that some credit card companies have begun the clean-up. But more needs to be done," said Republican Senator Norm Coleman. Mr Levin and fellow Democratic Senator Claire McCaskill hope to pass legislation next year to improve credit card practices. Mr Obama, who hopes to win the US presidency in 2008, said his proposed Bill of Rights would "crack down on predatory credit card companies using deceptive practices to make big profits while driving families deeper into debt." The bill, which he pledged to implement if he becomes president, would bar banks from hiking interest rates without giving consumers the option to opt out of an contract among other protections. Lawmakers expressed concern that some banks use a process called Universal Default to justify sudden and sometimes sharp interest rate hikes on credit card bills. Under Universal Default, a bank can automatically hike a consumer's interest rate if they are late paying a bill to an unrelated third party such as a department store. But the term is a cause of dispute between some lawmakers and consumer groups who use it and banks who say they rely on "risk-based repricing." Capital One says it does it not practice "any form" of Universal Default while a Discover spokesman said the company uses a range of "risk-based" factors to oversee customers' accounts. Citigroup, America's second-largest banking group by market worth, stopped using Universal Default this year while Chase, part of JPMorgan Chase is in the processing of abolishing it. Congressional investigators found the interest rate on Ms Hard's Discover credit card suddenly jumped to 24 percent from 18 per cent last year. The rate spike meant that $US176 of her regular $US200 dollar payments to Discover were eaten up in finance charges while only about $US24 was put toward paying off her debt of over $US8000 dollars. Mr Levin said neither Discover or the congressional investigators could work out why Ms Hard's rate spiked, but investigators suspect it was tied to a late payment on a department store credit card which lowered her credit rating. Banks track customers' spending, debts and other financial relationships through reports compiled by the Fair Isaac Corporation which also produces influential credit ratings on millions of Americans. "The credit scoring process is akin to a black box; no one knows exactly how it works or what lowers a score, yet it has become the primary driver of interest rate increases for tens of millions of Americans," Mr Levin said. Bruce Hammonds of Bank of America said the bank could make it clearer to consumers that they face potential rate hikes if they are late paying a bill to another party. The American Bankers Association (ABA) meanwhile warned Congress that new legislation could have "unintended negative consequences," and said it was a myth that Americans were drowning in credit card debts. The ABA says most Americans pay their credit card bills in full every month, that the credit card industry has become more competitive, and that many banks no longer charge annual fees on their cards.