CINCINATTI – The country’s largest supermarket chain, Kroger Co., is launching an in-house grocery delivery service. Kroger Ship, as it’s called, will be serviced by Vitacost.com, a health-products and natural-foods e-commerce site, that the grocer acquired in 2014.

Kroger Ship will offer 50,000 shelf-stable products in four cities this month—Cincinnati; Houston; Louisville, Kentucky; and Nashville, Tennessee—and eventually will expand nationally where no physical Kroger stores exist. During the launch, customers will receive free shipping with no minimum purchase required and a 15% discount code.

Once the service is established, it will offer $4.99 flat-rate shipping, which will be waived for orders of $35 or more. The site also will offer 5% discounts for subscription goods—aimed at retaining repeat customers.

Kroger Ship is the company’s fourth ecommerce platform launched in less than three months, and comes at a competitive time when Amazon and Walmart’s e-commerce options are eating into grocers’ sales.

“The customer is changing rapidly,” said Yael Cosset, Kroger’s chief digital officer, in an interview with the Wall Street Journal. “It is creating a sense of urgency and huge opportunity for us. … I don’t think five years ago we would have said delivery was critical.”