There is now a new tenant setting for Power BI admins to prevent users from creating classic workspaces in Power BI! This includes from places like MS Teams! Hurrah!
If you’re a Power BI Admin you can now enable ‘Block classic workspace creation’.
To do this go to the powerbi.com portal and click the ‘settings’ icon in the top right hand corner of the screen.
Click on ‘Admin portal’ and then locate and click ‘Tenant settings’.
Next under the ‘Workspace settings’ click ‘Block classic workspace creation’.
Now change the toggle from ‘Disabled’ to ‘Enabled’. This will now block the creation of new classic workspaces in your Power BI portal from places like MS Teams.

This will also automatically remove classic workspaces from your Power BI workspace list, but only if they were created by Teams, and only if they’ve never been accessed. If they have been accessed then they’ll be left there for you to deal with manually.
Now you’re probably thinking well I’ll just delete any old remaining workspaces which have been accessed but are no longer being used! Woah hold on…If you do this you’ll end up deleting the underlying office 365 modern group (and the associated Team!) which still may be used.
A better way of doing this is to upgrade the workspace to the new experience and then delete it.
To do this, click on the ellipsis next to the filters button within the workspace you want to delete and click ‘Edit workspace’. Next go to the advanced section and under ‘Upgrade this workspace (preview)’ select ‘Upgrade now’.
A small window will appear in the middle of your screen.
Check the ‘I’m ready to upgrade this workspace’ option and then click ‘Upgrade’.
Now, once the workspace has been upgraded to the new experience you can then click on ‘Settings’ icon and click ‘Delete Workspace’. This will now leave the office 365 modern group untouched but remove it from your workspace. Simple!
As always a big thanks to the guys from at Guy In A Cube (Twitter: https://twitter.com/GuyInACube) on You Tube for sharing this knowledge!
Check out their video here: https://www.youtube.com/watch?v=T2PAL4D2SvU.
Here’s the link to the Microsoft Power BI team’s announcement on this new feature: https://powerbi.microsoft.com/en-us/blog/announcing-you-can-now-block-classic-workspace-creation/