Citigroup

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and

American Express

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are joining forces to issue a new credit card.

The new card will be issued by Citigroup, but will be accepted by merchants that are part of the American Express network, according to a press release. Citibank will be responsible for handling and billing customers.

The companies did not disclose the financial terms of the partnership.

The deal between the two financial services firms reflects the changing landscape in the credit card business following a federal antitrust ruling against

MasterCard

and

Visa

. In a landmark case, a New York federal court found that the two big credit card associations had engaged in uncompetitive business practices that had a negative impact on American Express and other card companies.

The court specifically struck down a rule imposed by Visa and MasterCard that had prohibited member banks from issuing cards from other companies. The Supreme Court, in October, refused to overturn the court's ruling.

In the wake of the court decision, American Express filed suit last month against eight banks that allegedly conspired with MasterCard and Visa to engineer a boycott of American Express' charge card. The lawsuit named most of the nation's major banks, but not Citigroup.

At the time, analysts on Wall Street were puzzled by American Express' decision not to name Citigroup as a defendant.