In the Your CloudWok overview there are two lists, your active CloudWoks and your inactive CloudWoks. Uploads are only possible to active CloudWoks. So deactivating is a good way to stop users from uploading for example when the submission period for the files is over.
To deactivate a CloudWok just use the Deactivate button in the Settings of a Wok. To activate it again use the Activate button in the same place.
After a Wok was deactivated uploaders accessing the referring URL will be informed about this page not being available.