A single word for "not allowed to be changed" or "must be this way"

I'm looking for a specific word (that is slipping my mind) that means "not allowed to be changed" or "has to be taken as law". The word I'm thinking of sounds something like "invaluable" or "inviable". An example of how to use it would be "Since the CEO likes it, this feature is ___ "

You can use the adjective immutable:

unchanging over time or unable to be changed.

Got it- the word is "inviolable"

Definition from Merriam Webster:

1: secure from violation or profanation
2: secure from assault or trespass

"Inviolable" at first glance doesn't precisely fit my example sentence: "Since the CEO likes it, this feature is ___ ". However, when emphasizing the importance of the feature in question- to the point of making it sacrosanct- the word works.

Stretching the definition of "single word" slightly, and it doesn't sound like the word you were thinking of, but perhaps (depending on the context) non-negotiable might do?

Since the CEO likes it, this feature is non-negotiable.

Which would work well if the context is something like:

We need to remove some features from this release due to time constraints. Can <this feature> be removed?

Sorry, since the CEO likes it, this feature is non-negotiable.