American Express Co.'s credit card delinquencies are rising faster than expected, reaching the highest since the 2001 recession, and potentially pushing the stock lower, according to a research note from Friedman, Billings, Ramsey Group Inc.

Amex's delinquency rate rose 29 basis points, to 3.71% in August, while the default rate rose 51 basis points, to 6.14%, Friedman analysts Scott Valentin and Ram Gowrisankaran wrote in a research note that was published Monday.

Cardholders are struggling to repay their debt as the job market falters, unemployment rises and the cost of living is increasing at the fastest pace since the recession of 1990 and 1991.

The analysts predicted that these factors would affect the company's stock. "A challenging macro environment will lead to higher-than-expected credit costs over the next six to nine months, causing the shares to decline from current levels as investors realize American Express is more credit sensitive than anticipated," they wrote.

Cash-strapped customers are not the only problem. About 32% of Amex's debt will mature in the next six quarters and banks and investors will likely charge American Express more to borrow, the analysts wrote.

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