first thing that comes to mind is asking your IT team to block the URL temporarily or you can deactivate all your users either manually or via CSV import depending on how many you have.
If you want to have full control over the logins and are a SuperAdmin, I’d suggest to use the user-deactivation via csv. However, depending on your situation, there are a few points to be careful with. If you have registered users that actually are supposed to be deactivated, be careful not to reactivate them. And, it might sound stupid, don’t deactivate yourself via csv (yes, that’s possible)!
What I would do: download a complete user list with their status (active/inactive). Then use that list to deactivate the active users (except your account) via csv upload. Afterwards, you can use the same list again to reactivate the users. It’s actually very easy.