Labor does not support cutting penalty rates. Plenty of people rely on penalty rates as a regular part of their income - like hospitality workers, retail workers, nurses, police, and firies, among others. The Liberals have been at best weak on defending penalty rates, and some of them have openly called for people's penalty rates - and therefore their take-home pay - to be cut.
Bill Shorten gave a major speech this week committing a future Labor government to protecting penalty rates. You can read about it here.