Microsoft has banned the use of the free version of Slack for its 100,000+ employees. GeekWire reports that Microsoft has a list of prohibited apps and services, and even Amazon Web Services (AWS) and Google Docs are “discouraged for use” inside the company. The Slack ban isn’t primarily driven by Microsoft’s competing Teams product, though. Microsoft is reportedly concerned about the security aspects of Slack Free and Slack Plus. An internal entry describes the situation:

“Slack Free, Slack Standard and Slack Plus versions do not provide required controls to properly protect Microsoft Intellectual Property (IP). Existing users of these solutions should migrate chat history and files related to Microsoft business to Microsoft Teams, which offers the same features and integrated Office 365 apps, calling and meeting functionality. Learn more about the additional features that Teams can provide your workgroup. Slack Enterprise Grid version complies with Microsoft security requirements; however, we encourage use of Microsoft Teams rather than a competitive software.”

Slack Enterprise Grid is the only version approved for use

That means employees can use Slack Enterprise Grid, but given the costs involved it’s far more likely that most groups in Microsoft will be using the preferred Microsoft Teams option. AWS and Google Docs usage will reportedly “require a business justification” for employee use, and even Microsoft-owned GitHub is discouraged for “Highly Confidential types of information, specs or code.”

Microsoft has also banned Grammarly inside the company, which is a writing and grammar-checking app that can monitor every keystroke. “The Grammarly Office add-in and browser extensions should not be used on the Microsoft network because they are able to access Information Rights Management (IRM) protected content within emails and documents,” according to the leaked list.

Microsoft’s prohibited list makes a lot of sense for security-related matters, but employees still need to use these competing services to further their own products and understand the broader market. That would be a key part of any business justifications to get access to services like AWS or Google Docs.

Microsoft has been competing with Slack aggressively, but the messaging service recently launched apps and integrations for Slack and Office 365 to bridge the gap. Microsoft also launched its free version of Teams to rival Slack earlier this year, just weeks after the company unveiled creative new conference call features for its Slack competitor.