Blue Cross and Blue Shield of Illinois, the state’s largest health insurer, soon will no longer administer claims and provide customer service to employees of Wal-Mart Stores Inc., the world’s largest retailer, losing the business to another Blue Cross plan in Arkansas.

Starting in January 2010, Illinois Blue Cross won’t be performing administrative functions, such as staffing customer-service call centers, for employees of Wal-Mart, the health plan confirmed. Wal-Mart employees in the state still should be able to access benefits through Illinois Blue Cross because the new contract is largely related to behind-the-scenes work, the insurer said.

Such administrative tasks will begin in 2010 to transition over to Arkansas Blue Cross and Blue Shield, Illinois Blue Cross said.

Illinois Blue Cross would not disclose the financial impact of this change. Bentonville, Ark.-based Wal-Mart has more than 1.4 million U.S. employees and is known for its clout in negotiating with its many vendors.

“The membership in our four states will still be captured as part of our market share,” Illinois Blue Cross spokesman Jack Segalsaid of its parent, Chicago-based Health Care Service Corp., which also operates three other Blue Cross plans in Oklahoma, Texas and New Mexico.

In its new role, Health Care Service’s four Blue Cross providers will “become what’s known as ‘host plans’ for Wal-Mart’s approximately 200,000 members that live in our four states,” Segal said. “As host plans, we’ll provide our [medical-care provider] networks and our discounts, continue to reimburse providers and continue to determine claims pricing.”

As a home plan, Illinois Blue Cross has 445,000 members at Wal-Mart.

Wal-Mart would not confirm the change in the contract or financial terms of its relationships with any of the Blue Cross plans that process its health care.

“We regularly assess the quality and costs of the health-care plans offered by our providers, including those plans owned by Health Care Service Corp., and we don’t have any changes to those plans to announce at this time,” said Greg Rossiter, spokesman for Wal-Mart.

But Illinois Blue Cross said, “Wal-Mart was looking to consolidate into a single platform, so Arkansas [Blue Cross] decided to take this on and become the single home plan or administrator.”

Until the transition, Illinois Blue Cross will continue to share administrative duties with the Arkansas Blue Cross plan and Blue Cross and Blue Shield of Alabama.

Health Care Service had $865 million in net income last year on $14.3 billion in premium revenue. The nation’s fourth-largest insurer, the Chicago company has 12.4 million members, including 7.4 million in Illinois.