Are there any restrictions to an employee undertaking secondary employment with another employer whilst on parental leave under Fair Work legislation? Or is this be dependent on what is stated in workplace policies or the individual’s employment contract?

Generally speaking, an employee cannot take up paid work with another employer whilst on unpaid parental leave without their original employer’s consent. Although this is not specifically provided for in the Fair Work Act, the eligibility requirements for unpaid parental leave state that an employee must be the child’s primary caregiver. It is arguable that the employee ceases genuinely being in need of unpaid parental leave where they have taken up employment elsewhere as they are no longer taking the leave to primarily care for their child. If you wished to regulate this, you could state this in a company parental leave policy.