Meredith Whitney, the banking analyst at Oppenheimer & Company, recently predicted that card companies would reduce credit lines by $2 trillion, or about 45 percent of all available credit, in the next 18 months.

Here, cardholders have a bit more control. In reducing credit lines, companies may be looking for people who are already using a large percentage of their available credit. Try to avoid doing this if possible.

NEW FEES Several years ago, Martin Rodriguez, a resident of Quincy, Mass., transferred balances onto two Chase credit cards in response to offers promising low interest for the life of the loan. Recently, however, Chase sent him a note informing him that he would need to raise his monthly payments and turn over a $10 monthly fee to keep the low rates on his $20,000 in debt.

To Mr. Rodriguez, “life of the loan” ought to mean just that. “I’m searching for a legal boundary here,” he said. “If you read the fine print, I would have been better off going to Tony Soprano for a loan.”

Paul Hartwick, a Chase spokesman, said in an e-mail message that the terms and conditions of the card allowed the company to make such a change. He also said that these changes affected less than one half of 1 percent of its accounts and were aimed at those who had carried large balances for more than two years while making little progress in paying them off.

But Robert J. Lahm Jr., who lives in Candler, N.C., said that he had paid off almost half his Chase balance and still got the same notice as Mr. Rodriguez. And besides, he argued, any prudent person would delay paying off this sort of permanent low-rate loan, as he had while repaying higher-interest student loans he took on while completing his doctorate.

Mr. Hartwick said he stood by his statement and declined to comment on a class-action lawsuit that was filed in California this week over the issue.