Hello I am going to help you with your inquiry.

You seem to be in a position of either having to decide whether you wish to resign due to this action by your employer and seek an unfair dismissal remedy or whether you wish to terminate your contract and seek a contractual remedy. Your employer has done something that may be in breach of your contract of employment with them. If you just let it happen, it could amount to a waiver of your rights to sue for the breach of contract. If you don't let it happen you may be able to seek damages in Court. Whether you should, alternatively, seek an unfair dismissal remedy will largely depend upon your salary level. There is a threshold above which you cannot access this remedy. The threshold is $136,700 not including superannuation.

There may also be terms in the employer's unpaid leave policy or the contract dealing with yours and the employer's rights in this situation.