Used to express what should not be done; 'must not', 'should not'.
Long explanation:
The Japanese grammar point Verbる べからざる Noun is used to indicate something that should not be done, or is not allowed to be done. It translates to 'must not' or 'should not' in English. It is often used in formal written Japanese or in formal speeches. It is constructed by using the verb in its dictionary form followed by 'べからざる' and a noun, usually behaviour or event.