Credit card companies including American Express ( AXP), Capital One Financial Services ( COF) and Discover Financial ( DFS) are overpriced these days, according to one boutique investment firm.

Given the recent run-up in financial stocks since early March due to increased investor optimism about bank profits, the economy and regulatory/political issues, Stifel Nicolaus analyst Christopher Brendler downgraded the credit card companies on Tuesday.

He lowered his rating on American Express to sell from hold and on Capital One and Discover to hold from buy. He had upgraded the stocks in March.

Shares of American Express have nearly doubled over the last month. The stocks of Capital One and Discover rose 59% and 47%, respectively, since the end of February, Brendler writes in company notes.

" I t is an opportune time to step aside," Brendler writes in an industry note. "While we still see this group as survivors, the key question remains the timing of a turn in the economy. In our view, just as the market was overly bearish a month ago, it now appears overly optimistic that a turn is imminent."

Brendler says that the full effects of a sharp rise in unemployment have yet to be realized in the economy and is concerned that "this will lead to another leg down in housing and credit quality, possibly reigniting fears of a prolonged deep recession," according to the note.

He adds that credit card losses are expected to rise significantly as recent data showed "accelerating deterioration partially due to rising bankruptcy filings," according to note.

"While we are still optimistic that card losses will rise only slightly above unemployment, we believe the risks are clearly weighted to the downside," he writes.

American Express was downgraded by Goldman Sachs to a sell rating in March.

Capital One and American Express are expected to report earnings next week.

Discover's fiscal year ends in November as opposed to December. Last month, it reported a boost in profit for the first quarter, largely based on gains from litigation settlements with Visa ( V) and MasterCard ( MA). Still, the company slashed its dividend by two-thirds to 2 cents a share to conserve capital.

Discover also plans to reduce its workforce by 500 positions, according to media reports.

Shares of American Express were down 2.2% to $20.02, Capital One shares were losing 17 cents to $19.04 and Discover shares were falling 4% to $8.11 on Tuesday.

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