Only the Key Account Holder or an Admin User of your account can set up a setting called Global Tags Only so that ad-hoc tags cannot be created. Please see the steps below to set this up:

1. Go to the Settings icon along the top of the menu bar inside your CRM:

2. Click on the Global Settings tab as shown below:

3. Here you will see a check box called Global Tags Only?  As shown below:

4. Place a check inside this box as shown below:

5. Click on the Update Settings button to save

6. Now only global tags can be created. 

Please note: that only the Key Account Holder or Admin Users of your CRM have access to Global Settings to create global tags.