Metlink general manager Scott Gallacher said the union meeting will not affect school services but will impact some customers using off-peak services.
"Tranzurban is working hard to cover as many driver shifts as possible, to minimise any possible disruptions.
"We will keep customers updated through our website and social media channels, as well as through public information on radio."
Gallacher said whilst some services might be impacted, Metlink fully supports any union members attending the meeting.
The following services will be impacted: 110, 111, 112, 113, 114, 115, 120, 121, 130, 145, 150, 154, 160, 170.
