Frank Chan said he had been a loyal Citibank cardholder for 20 years when he was told by a customer service agent that stopping a check payment would cost him $29.

He said he was shocked to see on his next credit-card statement that as a result his interest rate had more than doubled, from 13.9 percent to 28.9 percent, and applied to his current balance.

Citigroup Inc., the biggest U.S. credit-card lender, agreed to remove the extra interest charged, yet for Chan it was too late.

"I was so angered by their sneakiness that I paid off and terminated my Citicard account immediately," said Chan, 43, a religious studies professor from New City, N.Y.

Citigroup declined to comment on the specifics of his case.

A bill pending in Congress seeks to protect credit-card users from these kinds of sudden rate increases and fees.

The legislation, approved by a committee in the House, requires 45 days notice of interest rate increases, prohibits companies from changing the terms of the contract at any time for any reason, and makes issuers mail billing statements 25 days before the due date, instead of the current 14-day minimum.

Consumer advocates say it will give cardholders more control and prevent them from spiraling further into debt.

Industry groups say there will be unintended effects of the measure, especially for consumers who pay their bills in full and on time.

"Less risky borrowers will have to absorb the costs posed by riskier borrowers if issuers can't price everyone based on the risk they pose," said Ken Clayton, senior vice president of card policy at the American Bankers Association based in Washington, D.C. Card applicants perceived to be high-risk because of low credit scores may no longer qualify if the legislation passes, he said.

With declining home equity limiting access to credit, more Americans are relying on plastic. Consumer credit-card debt is nearing the $1 trillion mark, which is double the amount held in 1996, said Rep. Carolyn Maloney, a New York Democrat who is sponsoring the bill, in an e-mail.

"Now more than ever, we need to end unfair and deceptive credit-card lending practices that make it difficult for consumers to control their credit and manage their debt," said Maloney.

About 60 percent of cardholders don't pay off their balances each month, said Ben Woolsey, director of marketing and consumer research at CreditCards.com, an online resource for credit-card users.

The percentage of credit-card debts that were unpaid after at least 30 days rose 22 percent this June over a year earlier, averaging 4.03 percent, based on reports filed by American Express Co., Bank of America Corp., Capital One Financial Corp., JPMorgan Chase & Co., Citigroup and Discover Financial Services.

The average interest rate charged on existing credit-card balances was 13.5 percent, according to the Federal Reserve's June G19 report, which tracks rates for credit-card accounts.