Say that an action is forbidden.
The rule
Word in て + はいけない means "do not / it is forbidden from". The polite form is ～てはいけません.
Examples
ここでたばこをすってはいけません。
You can't smoke here.
ここにはいってはいけません。
It is forbidden to enter here.
Remember
- てはいけない ≠ なくてもいい: prohibition ≠ no obligation.
- Say that an action is forbidden.
Common mistake
Say てはいけない for "you are not obliged": the meaning becomes "prohibited".