Although the strike is being carried out by NBRU members, Bus Eireann spokesman Andrew McLindon said it appeared members of other unions, SIPTU and the Transport Salaried Staffs' Association, were not passing pickets.
Derry, which will be UK City of Culture 2013, was a late confirmation on the shortlist after the Ulster Council of Comhaltas Ceoltoiri Eireann reversed its previous decision not to support the bid.