I don’t think there is a contractual need to notify an early warning in this situation. It would not seem as though anything could be done about it anyway - which is the whole point of an early warning i.e. what can we do about it.
Whatever you call it though - it would do no harm to let the Employer know this increase is coming just so they can understand increased costs/manage expectations elsewhere - it just doesn’t need to be on a piece of paper called an “early warning”.