Belfast bus drivers plan to stage a series of protests throughout the city in a row over dedicated bus lanes.
Metro drivers are calling for a ballot on action
The union, Unite, said Metro drivers were calling for a ballot for industrial action.
This was to highlight the difficulties of providing a "first class transport system with uninterrupted bus lanes".
Last week the union called on Minister Conor Murphy to meet promises made to introduce dedicated bus lanes into the city centre.
Drivers said they were under constant stress to meet unrealistic running times during peak periods of congestion.
Unite said its representatives were expected to meet the minister next month.
It questioned how long the Rapid Transport System outlined by the Department for Regional Development would take to come into effect.
Unite's Sean Smyth said: "The drivers also ask, how can the minister plan a new Rapid Transport System without priority lanes - whether for buses or a light railway or a mixture of both?
"Without priority lanes being in operation neither system, as being experienced by the Metro bus service at the moment, will not work."