In a court filing, the Department of Justice has revealed the degree to which it is relying on private litigation against Visa U.S.A. and MasterCard International to support its own case against the two bank-owned associations.

Several months ago, the government won the right to obtain the discovery documents in what is known as the Wal-Mart lawsuit-a class action filed by major retailers against Visa and MasterCard, attacking their debit card rules.

The federal antitrust enforcers, whose suit focuses on credit cards, now wants the private notes and analyses that the debit-case plaintiffs have gathered over the past two-and-a-half years.

Last week in federal court in Brooklyn, N.Y., the government filed a motion to intervene to modify a protective order that safeguards the confidentiality of those documents.

The idea is that obtaining the plaintiff attorneys' notes would significantly reduce the work load of the government's lawyers.

"They know we are two years ahead of them in terms of analysis," said Lloyd Constantine of Constantine & Partners, the New York law firm representing the retailers. "It's somewhere between 50,000 and 100,000 hours of work we have done."

Noah Hanft, senior vice president and counsel for MasterCard, said: "The terms of the protective order were negotiated by all parties in good faith. We see no basis for modifying that agreement and intend to oppose the motion."

The Department of Justice, which filed its lawsuit against Visa and MasterCard in October, began focusing on debit cards in January, after the Federal Trade Commission transferred its investigation into the bank card associations' debit cards to Justice.

At issue are Visa and MasterCard rules forcing merchants to accept their credit and debit cards on roughly the same terms. Merchants argue that debit transactions are less risky, because the funds are deducted directly from cardholders' bank accounts and should, therefore, cost less than credit card transactions.

The government suit seeks to accomplish two things: overturn card association rules prohibiting members from issuing competing card brands such as American Express and Discover, and change the governance of the associations to ensure that each of the largest issuers is aligned with either Visa or MasterCard, rather than both.

As the Justice Department's debit card investigation progresses, there is little doubt that debit cards will become central to its case against Visa and MasterCard.

Mr. Constantine said: "There is a high degree of coordination between us. We consider their participation to be helpful to our case."

But it is a one-way relationship. Mr. Constantine has sought twice to obtain the government's discovery documents and has been turned down in court each time.

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