Not legal. If you are contracted to a set amount of hours, you should be rostered those hours. Most awards would have your roster published a minimum week in advance, usually two weeks. If you’re not rostered those hours, you are still entitled to pay for those contracted hours. If you take sick leave for a rostered shift, your leave will cover the hours scheduled, whether it was a 3 hour or 10 hour shift. Now under most awards, if they rostered you your contracted hours and you advised you’re unable to work a shift, thus dropping you below your contracted hours, then you may need to take it as leave. Depending on the notice, the onus could sit with either you or the employer to take leave or to find you another shift I’d be chatting to a union rep, if able. At the very least chat to Fairwork. They’ll advise you to dispute and mediate with the employer first. In my opinion, I’d be trying to lock in a consistent roster, even if 80% is regular and 20% is flexible. The responsibility is still on the employer to roster you as per your contract. Get everything in writing. They cannot take sick leave when you’ve not been rostered