The imperative in the negative is formed by placing a 'non' before the verb for noi, voi and Lei
E.g
(Noi) non lavoriamo! - let's not work! (we)
(Voi) non lavorate! - Don't work! (you plural)
(Lei) non lavori! - Don't work! (you polite)

However, with forming 'TU' in the negative, you place 'non' before the infinite
E.g
(Tu) non lavorare! - Don't work! (you)
(Tu) non scrivere! - Don't write! (you)