With its antitrust trial against Visa and MasterCard only five days away, the Department of Justice appears to be stepping up its investigation of the credit card companies' debit card policies, which raises the question of whether the government will file a second lawsuit against the card associations.

Over the past couple of months, credit card lenders - including Citigroup - have received subpoenas from the government requesting documents about debit cards, say sources close to the banks. The government has also been working closely with lawyers for major U.S. retailers that have filed a class action against Visa's and MasterCard's debit rules and prices.

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