Canon sued for disabling scanner when printers run out of ink - https://www.bleepingcomputer.com/news/legal/canon-sued-for-disabling-scanner-when-printers-run-out-of-ink/
While using his Pixma MG6320 printer from Canon, the plaintiff was surprised to discover that the "all-in-one" machine would refuse to scan or fax documents if the printer ran out of ink.
As ink is not necessary to perform scans or faxes, the argument is that the printer features should continue to work even if there is no ink in the device.