(May 25) Wal-Mart Stores Inc. has altered its procurement procedures during the past two years, but recent criticisms that the Bentonville, Ark.-based retailer has violated terms of its supplier agreements are unwarranted, the company’s vice president and divisional merchandise manager for produce and floral said.

“Wal-Mart honors (its) contracts and offers the suppliers the right to talk to Lee Scott, our CEO, or Rob Walton, our chairman, through the open-door process if we do not,” said Ron McCormick , vice president and divisional merchandise manager for produce and floral.

Wal-Mart suppliers were reluctant to comment on changes in the retailer’s buying practices, but sources alleged off the record that the company is increasingly using what it calls “opportunity buys” to source product from other suppliers when the market is lower than the contract price.

“The expectation in doing business with Wal-Mart is not what it was two years ago,” said a supplier who spoke on the condition of anonymity.

The source said the practice offers suppliers no protection from depressed markets and allows the company to use its suppliers only when the contract terms and market conditions are favorable to the retailer.

McCormick, however, said Wal-Mart remains committed to buying 75% to 80% of its produce through contracts. He said the company uses spot buys to source the balance of its volume in order to take advantage of market opportunities and to test new suppliers. McCormick said the practice allows consumers to buy at low prices, increasing consumption and driving sales.

The most significant change during the past two years, McCormick said, is Wal-Mart’s shift from distribution center assignments — where a single supplier was responsible for providing a specific commodity to a specific warehouse — to what the chain calls “dollar value assignments.”

McCormick said a number of factors led to the demise of distribution center assignments, including the growth of the company’s consolidation facilities that allow the company to send full truckloads to its 38 food distribution centers.

“Our local purchase program also means that we have many more small growers we are doing direct business with, often combining them to meet the demand of a single (distributin center),” he said. “That single supplier per DC consistency no longer adds value, and actually impedes better customer service.”

Critics argue that the distribution center system provided suppliers with regular volume they could count on and a geographical reference point, but McCormick countered that Wal-Mart’s emphasis on “food miles” as part of its sustainability effort will ensure that suppliers are aligned with distribution centers that make geographic sense.