It's a command requirement for low capacity RPT. Refer CAO 82.3 Appendix 4:
Aeroplanes exceeding 5 700 kg MTOW
Air transport pilot (aeroplane) licence
Command (multi-engine aeroplane) instrument rating
2 000 hours total experience as a pilot, that includes:
500 hours as pilot in command (or acting as pilot in command under supervision) on multi-engine aeroplanes under the I.F.R.; and
50 hours as pilot in command (or acting as pilot in command under supervision) on the aeroplane type; and
100 hours experience as a pilot on night operations.