Depending on your organization’s business needs, there may be reasons that you do not want some users to be using Microsoft Teams within your Office 365 tenant. You can prevent users from using Teams either from the Office 365 Admin Center or by using Office 365 PowerShell commands. If using the Admin center, click on the waffle in the left hand corner,
then click on the Admin Center icon.
Click the arrow next to Users
click the checkbox for the user that you want to deny the use of Teams,
then drag the bar to Teams to turn it off and disenable it for that user.
If you prefer to use Office 365 PowerShell to perform this task, see this article:
More Info on Microsoft Teams Licensing: