Management cannot make you use your leave entitlements during the COVID-19 pandemic so casuals can have more hours.
If you have contracted hours and there’s enough work, you can be directed to work either in your area or in another one as long as it’s within your scope of practice.
Don’t be bullied or harassed into taking your leave if you do not want to.
In your agreement, there’s a clause that says you can only be made to take leave during close down periods, which are listed as the months of December and January. There’s no COVID-19 related exception.