There are two options that a folder owner can set on a folder in order to prevent their collaborators from inviting new collaborators .
To use these features click on the little box with the downward arrow next to the folder and select 'Properties' > "Security".
On the small pop-up window you'll see a "Restrictions" section.
Two of the settings 'Only Owners and Co-Owners can send collaboration invites" and "Hide Collaborators" will allow you to prevent collaborators from inviting other collaborators. Click 'Okay' to complete the selection.
You'll notice, when choosing "Hide Collaborators", the first option is automatically checked for you. This is to protect the integrity of a hidden collaborative environment.