Identifying "fake news" in a non-partisan way is required for the consequences of such a law to be non-partisan, but is probably not possible with real humans. So instead you would get a Ministry of Truth that identifies fake news as that which is disapproved of by the party.
The Russian state is currently busy crushing independent journalism in just that way with their recent fake news law.
The Russian state is currently busy crushing independent journalism in just that way with their recent fake news law.