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AmEx shares spike on large ValueAct stake

Shares of American Express spiked in midday trading Friday after news that activist fund, ValueAct Capital, had acquired a $1 billion stake in the credit card company.

Shares rose as much as 6.8 percent following the news. The stock is on pace for its best day since Nov. 2011 as long as the stock remains over 5.12 percent. So far, the stock has already tracked its best day since Aug. 2011.

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American Express provided the following statement to CNBC:

ValueAct is a well-respected firm. We have been speaking with them, as we do with other investors, and look forward to continuing a constructive dialogue. At American Express, we are focused on building long-term value for shareholders, and are always open to the views and perspectives of our investors.

ValueAct did not immediately respond to CNBC's request for comment.

The hedge fund's stake would account for just over 1 percent of AmEx, based off Thursday's close.

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This is dwarfed by a 15 percent holding in the company by Warren Buffett's Berkshire Hathaway.

AmEx, which caters mainly to wealthy corporate clients, has been cutting costs to cope with stiff competition that lost it a couple of lucrative co-brand contracts.

The company recently lost an exclusive tie-up with warehouse club operator Costco. AmEx said in February that the loss would hurt earnings for the next two years.

—Reuters contributed to his report.