Walmart Inc. has begun telling online shoppers that some products in its warehouses are “out of stock” after the retailer changed its e-commerce systems to avoid orders deemed too expensive to ship.

The change means that a bottle of detergent or can of cat food stored too far away from a customer’s shipping address will be unavailable for purchase. Previously, the retailer would ship those items, regardless of distance or shipping cost.

The new system, introduced earlier this month, has led to a decline in sales at some companies that sell their products on walmart.com, according to executives at Walmart suppliers. Some suppliers weren’t warned of the change in advance, said these people. Under the new system, suppliers will have to stock their products at more Walmart warehouses around the country to keep sales steady, according to an executive at a large food company.

“I think long term it’s absolutely the right choice” to make shipments more profitable, the executive said. “Short term, it’s a bit chaotic.”

The shift is part of a test, Walmart said, to see if it can deliver more products via ground shipping, a cheaper option than air shipping, in two days or less and reduce what it calls split shipments — online orders that arrive in multiple packages from different warehouses, according to Ravi Jariwala, a company spokesman.