Visa, the biggest U.S. credit card network, on Friday took its first official step toward becoming a public company, the Associated Press reported. Visa filed a statement with the Securities and Exchange Commission outlining a proposal for restructuring to combine its global operations. San Francisco-based Visa plans an initial public offering to take place in early 2008. About half of its 775 million shares outstanding — now owned by the network’s member banks — would be sold to the public via the New York Stock Exchange.

Major rival MasterCard Inc. also decided to convert into a public company. It went public in May at $39 a share. The company is currently valued at about $22.5 billion.

Retailers have filed suit against Visa and MasterCard, accusing them of illegally fixing the transaction fees applied to merchants with every purchase. Legal experts say Visa’s offering will help insulate member banks from billions of dollars in potential judgments from antitrust claims brought by merchants.