If an employee has stored excess annual leave amounts, generally more than 3 years equivalent accrued leave (12 weeks is 3 times 4 weeks) though this is industry dependent as some industries with high levels of contractual work may have better tolerances to less breaks. If an employee is storing their annual leave in excess or for an extended time without a full break there may be underlying reasons and issues causing this to happen.
The employee may not feel supported enough to take leave in that there is insufficient succession planning or insufficient capacity for others to cover their role in the short term. If this is the case a conversation with the employee, their line manager and the HR team could look at alternate solutions such as internal short term relief from a different department or possibly external employees being brought in to cover the gap.
If there are systems in place for the employee to take leave and opportunities given but the employee declines and has excess leave accrued it may point to other less positive reasons such as a fear of competency failures in their role being discovered or in extreme cases wrongdoing.
Regardless of the reason an employee has to stockpile excess leave it is the organization’s responsibility to ensure that access and opportunity to take the leave is given as part of the health and safety policies managing burnout and workplace fatigue.
In some industry awards management can direct employees with excess leave to have compulsory breaks, refer to your industry award or employment agreement
In some industries scheduled or forced annual leave is possible, usually during the shutdown period of an organization usually around the Christmas and new year times or if an employee has accrued excess leave balances. Each industry and award agreement is different so check yours before placing an employee on compulsory annual leave.
Industry awards can be checked here. https://www.fairwork.gov.au/awards-and-agreements/awards/list-of-awards