How to say: you may not [verb] here?

たとえば、おすしを食べてもいいですか？ is for "May I eat sushi?".　However I know that ちょっと、食べなくてもいいです。Is not the right phrase because that means: "Well, you don't have to eat (that)." So what is the response for "[Sorry,] you may not eat sushi."?

Could you use this in response? おすしを食べることができません。

Also, one is this grammatically correct and two, is this saying what I think it means (you may not eat sushi)? おすしを食べてもよくないです。

I can't quite imagine that you have to say "you can't eat sushi here," i mean, you don't mean that it not available here (as in a restaurant) right? 

So i am going to use one of the most common examples for asking for permission:

- May I smoke here?
- No, you may not (smoke here).

ここで たばこを すっても いいですか？
いいえ、すっては いけません。or いいえ、いけません。

Please let me know if you mean something completely different, asking whether sushi can be eaten (meaning, is avallable) here.

Yes, your assumption is correct. I did not mean "is sushi available". My confusion came from the fact that "te wa ikemasen" in my studies was translated as "must not". So I didn't know if that was the correct response.


Just to reiterate, because I really am curious about this:

Also, one is this grammatically correct and two, is this saying what I think it means (you may not eat sushi)? おすしを食べてもよくないです。

おすしを 食べても よくないです。
...is not correct, unfortunately. 
This te-form + mo is used when asking it is OK, not in the response to that. You would say:
おすしを 食べては いけません。
おすしを 食べるのは よくないです。
The first one is the same "you must/may not..." structure, and the second is like "the act of eating sushi is not good."
I can think of a situation where you might say something using the structure in the second sentence, like:
きのうの よるの のこりの すしを 食べるのは よくないです。
(It's not good (for your health) to eat sushi left over from the night before.)