The battle for consumers’ dollars between the world’s largest retailer and the world’s largest e-tailer is heating up.

Following Amazon’s announcement of its $13.7B deal to take over Whole Foods Market, which has sent the grocery sector into a frenzy, Wal-Mart has told some of its tech vendors to get off Amazon’s cloud if they want to continue doing business.

Amazon Web Services accounts for about 40% of the world’s cloud services and houses the apps of several tech vendors that Wal-Mart uses. The retailer, wary of giving any additional business to its rival, has requested these vendors run their applications elsewhere, the Wall Street Journal reports.

In response to this move, an Amazon spokeswoman called the retailer a bully, saying “tactics like this are bad for business and customers,” the Journal reports.

Amazon is the biggest cloud-service provider in the world, followed by Microsoft and Google. The top three players have been upping their data center game, spending a combined $31.5B on their facilities last year. That is 22% more than they spent in 2015, and experts said their investment pace is not expected to slow as the companies continue battling over the $500B database technology business. Experts said the three firms are already so far ahead in data center investment and capabilities that it would be difficult for any would-be rival to challenge them — even Wal-Mart, which keeps most of its data on its own servers.