How to Say ‘May not do/not allowed to do…’ in Korean?

Verbs/Adjectives-(으)면 안 되다 expresses the prohibition or limitation of a particular action of the listener. It can represent social conventions or common sense dictating that a behavior or state is prohibited or not tolerated. It corresponds to ‘may not’ or ‘not allowed to’ in English.

When the stem ends in a vowel or ㄹ, -면 안 되다 is used, and when the stem ends in a consonant, -으면 안 되다 is used.

Example:

실내에서 담배를 피우면 안 돼요. Smoking indoors is not allowed.

지금 길을 건너면 안 돼요. You may not cross the street now.

-(으)면 안 되다 can be used in the double negative form, that is, -지 않으면 안 되다, to emphasize that a particular behavior must be performed.

Example:

8월은 휴가철이니까 비행기 표를 미리 사지 않으면 안 돼요. (=표를 미리 사야 돼요.)

August is vacation season, so (you) must buy plane tickets in advance. (Plane tickets have to be bought in advance.)

다음 주에 중요한 시힘이 있어서 공부하지 않으면 안 돼요. (=공부해야 돼요)

Because (I) have an important test next week, I must study. (I have to study.)