Genuine volunteers are not employees, however, somebody you call a volunteer may be legally considered an employee if certain conditions are met. This would mean that your organisation has an employment relationship with the volunteer (ie there is an implied contract of employment). There are various factors that determine whether there is an employment relationship. Two of the most important factors are:
whether the person is paid for the work they do - this is one of the strongest indicators that a relationship is an employment relationship. Therefore, when reimbursing volunteers for any expenses that they incur whilst volunteering for you, you should be careful not to pay them any more than the amount necessary to reimburse them for their expenses. Reimbursing volunteers for expenses that they have genuinely incurred by volunteering with you will not be considered ‘pay’.
whether there is mutual obligation between the parties - this can indicate an employment relationship if, for example, the volunteer is required to accept and perform work (eg if the volunteer must volunteer at certain set times) or if you are required to provide such work for the volunteer
Being sure that your volunteers really are volunteers (ie there is no employment relationship) is important if you don’t want to be obliged to pay them and to provide all of the benefits and rights (eg rights regarding dismissal) that employees are entitled to. This Volunteer Role Description template helps you to avoid creating an employment relationship. However, these situations can be complex. You should consider creating a Volunteer agreement to further clarify your relationship with your volunteers, or you can Ask a lawyer for help navigating the situation.
For more information, read Working as a volunteer.