Drivers for both companies have overwhelmingly voted in favour of strike action, in a row over plans which might result in the privatisation of some existing routes operated by the State-owned transport companies.
Senior union representatives are due to meet early next week to decide which form and timing any upcoming action might take.
The dispute centres around plans by the National Transport Authority to put to tender 10 per cent of the routes currently operated by Dublin Bus and Bus Éireann.
But unions have said that such tendering proposals could potentially lead to the privatisation of routes, and would result in a worsening of their members’ terms and conditions if private operators take over.