The annualized credit-card charge-off rate broke through 10% during May, according to Moody's Investors Service, the first time in the more than two decades the credit ratings company has tracked the measure.

Also, the measure of credit-card loans deemed uncollectible as a percentage of loans outstanding hit a fresh high for the sixth-consecutive month, rising to 10.62% in May on an annual basis from 9.97% in April and 6.41% a year earlier.

Credit-card operations at many banks are vulnerable as the unemployment rate has mounted amid the recession.

Bank of America Merrill Lynch, one of the nation's largest credit-card providers, saw its charge-off rate climb more than two percentage points from April, said Moody's.

Moody's senior vice president William Black said Moody's expects the rise in charge-offs to slow in coming months, though it continues to predict a peak of about 12% in the second quarter of next year.

The delinquency rate, or payments more than 30 days late, fell for a second consecutive month, to 5.97% from 6.34% in April, with a seasonal boost thanks the to tax-refund season. Moody's expects the rate to resume climbing.

But payments also slid for a second straight month, to 16% in May from 16.2% in April. Payment rates are likely to "remain soft" partly on lower purchase volume from consumers who use their credit cards for convenience and pay their balances each month, Black said.

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