Involved in peptidoglycan biosynthesis. Transports lipid-linked peptidoglycan precursors from the inner to the outer leaflet of the cytoplasmic membrane. Cell wall biogenesis; peptidoglycan biosynthesis. FtsW (AC P0ABG4) is also proposed to act as a lipid II flippase. The identity of the lipid II flippase is controversial with conflicting in vivo and in vitro results. Belongs to the MurJ/MviN family.