Visa Inc., the world's largest credit-card company, said the U.S. Justice Department has opened its fourth investigation into a credit-card fee paid by retailers.

The Justice Department's document requests ``focus on certain Visa U.S.A. policies relating to merchant acceptance practices, including Visa U.S.A.'s policies regarding merchant surcharging and merchants' ability to steer customers to other forms of payment,'' Visa said in a filing today with the Securities and Exchange Commission. Visa said it's cooperating with the investigation.

Just last month, I posted that Visa and rival MasterCard Inc. settled with Discover Financial Services over a lawsuit accusing them of blocking banks from issuing their cards. A U.S. district judge ordered Visa and MasterCard in 2001 to stop forcing banks to choose between their cards and ones from Discover and American Express Co. Her order followed a Justice Department suit against the credit-card groups for antitrust violations. Visa sued in 2004, after the U.S. Supreme Court refused to hear the case.