Disable free access to public teams

Hi MatthiasRepy. Do you now want the team to be Private and control who is a member? 

Change the team to Private.

Post a message to all members telling them you are restricting access and that members will be removed from the team.

Then remove the members you longer want to access the team.

 

 The challenging part is clearly explaining why you are restricting access and removing members, without causing confusion.

Hello,

In case you are referring to the Personal Teams Application it can be disabled from the following settings

Login to Teams Admin Center > Users > External Access > Uncheck Skype Users.

With Regards,
Satish U

You mean prevent users from joining (or accessing content) within already created Public teams? I'm afraid that's not possible. You can limit the creation of new teams if needed, or use container labels/default label requirement to limit the creation of Public teams.