Shares of all four major card networks have fallen sharply this week with the slowing economy pushing down consumer spending.

Consumer purchases fell 1.2% last month, according to data the Commerce Department released Wednesday.

On Wednesday, Visa Inc.'s stock price dropped 14%, to close at $49.75. The trend continued Thursday; at midmorning Visa's shares were down 2.29%, to $48.61.

Discover Financial Services lost 15% Wednesday, to close at $10.02, and the stock was down 5.69% Thursday morning, to $9.45. American Express Co. dropped 13% Wednesday, closing at $24.41, and slid 8.64% Thursday morning, to $22.30.

MasterCard Inc. fell 12% after the Commerce Department numbers came out Wednesday, closing at $153.55, and fell 5.22% Thursday morning, to $145.54.

"If consumers are spending less, MasterCard and Visa will get hit," said John Williams, an analyst at Macquarie Capital.

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