Days after arch-rival Amazon announced plans to buy Whole Foods for $13.7 billion, Walmart is apparently ramping up its defense.

That acquisition takes square aim at Walmart’s bread-and-butter grocery business by giving the online retailer 465 new retail locations—thus a much bigger brick-and-mortar presence.

Now, Walmart is telling some partners and suppliers that their software services should not run on Amazon Web Services cloud infrastructure, according to the Wall Street Journal.

The report quoted Bob Muglia, CEO of Snowflake Computing, saying that a Walmart wmt partner wanted to use his company’s data warehouse service, but was told it had to run on Microsoft msft Azure cloud instead of AWS.

Related: Walmart Wants to Unchain Retailers From Their Cloud

Currently, Snowflake’s software runs only on AWS.

Get Data Sheet, Fortune’s technology newsletter.

In an emailed statement, an Amazon amzn spokesman said: “Yes, we’ve heard that Walmart continues to try to bully their suppliers into not using AWS because they have an incorrect view that AWS is somehow supporting Amazon’s Retail business.”

Many suppliers are standing up to Walmart on this front, he added.

A Walmart spokeswoman said that the company’s vendors can use any cloud provider that meets their, and their customers’ needs but “it shouldn’t be a big surprise that there are cases in which we’d prefer our most sensitive data isn’t sitting on a competitor’s platform.”

Snowflake could not be reached for comment.

Related: Amazon Buying Whole Foods Could Boost Cloud Business

Actually, this is a flare up of an old story. Walmart has long used competitive cloud computing technology based on OpenStack and other open-source technology for its workloads. Other retailers—including The Gap, eBay, and PayPal—have also talked about their use of OpenStack.

That computing project was launched by NASA and Rackspace eight years ago to act as a counterweight to the growing power of AWS in public cloud.

Related: OpenStack Struggles in Public Cloud Wars

In the past, Amazon has touted many retailers including Nordstrom and Instacart that use AWS computing, storage and networking services, and that the computing arm operates separately from the parent company’s retail business.

Note: (June 21, 2017 11:45 a.m.) This story was updated to include comment from an Amazon spokesman.

Note: (June 21, 2017 11:00 p.m.) This story was updated to add Walmart comment.