An employer can postpone parents' leave when they feel it would have a ‘substantial adverse effect on the operation of their business, profession or occupation’.

Reasons for postponement can include:

(a) The seasonal variations in the volume of work
(b) The unavailability of another person to carry out the duties of the employee during the leave period
(c) The nature of the duties referred to in (b),
(d) Staffing levels over the period of the requested leave

Your employer may postpone the requested leave, but they must let you know in writing no later than 4 weeks before the intended start date of the leave.
The leave cannot be postponed for more than 12 weeks after the start date of the requested parent’s leave, and the new date must be agreed by both of you. Before
postponing the parent’s leave with a written notice, the employer must consult with the employee.

• The notice must contain a statement summarising the grounds for postponement.
• The leave cannot be postponed more than once.