Siptu has apologised to the estimated 60,000 commuters affected by a Dublin Bus drivers' picket at Harristown garage today over new route scheduling.
Branch organiser Willie Noone said the union, along with the National Bus and Rail Union (NRBU), was striving to find a solution to the dispute and restore services as quickly as possible.
But, he insisted: "no sustainable settlement is possible on the basis of simply imposing poorer conditions on Dublin Bus drivers".
Willie Noone of Siptu
More than 100 drivers at the north Dublin garage began industrial action this morning in protest at the planned rollout of two new bus routes due to start today - the 4A from Ballymun to Stradbrook and 128 from Clongriffin to Rathmines.
Pickets were placed on the garage after a female driver, who refused to drive a bus on one of the new routes, was suspended by Dublin Bus management.
The drivers are also opposed to new scheduling that means they will have to start, break and finish work in the city centre.
Speaking to ireland.com, NBRU acting general secretary Michael Faherty said the protest had "nothing to do with breaks - it's to do with where the drivers start and finish their day's work".
Mr Faherty said rostering arrangements - in place at Harristown garage for three years - were being changed and causing "operational difficulties" for drivers who will now have to make their way into the city centre from Harristown garage to begin their work.
But a Dublin Bus spokeswoman, Clíodhna Ní Fhatharta, told ireland.com: "We're not asking them [drivers] to do anything different to what any other driver is doing."
Ms Ní Fhatharta said Dublin Bus has deferred its plans to start the new routes twice since January this year to allow for further talks with the union at the Labour Relations Commission (LRC).
The LRC had now backed the company's plan and given it the go-ahead to start the routes, she added.
The NRBU said it had rejected the LRC's decision by 58 per cent and insisted drivers will stay on strike until a resolution to the dispute is found.
Mr Faherty also said he was aware of unofficial plans by drivers to spread the picket to Dublin's other six garages tomorrow but said the union is not sanctioning the move.
Dublin Bus said it is appealing for drivers not to take this step. "This has nothing to do with the other garages. It is irresponsible," Ms Ní Fhatharta said.
The main areas being affected today are Finglas, Swords, Ballymun, Blanchardstown, Donabate, Portrane, Dunboyne, Little Pace, Tyrrellstown, Damastown, Portmarnock, Kinsealy and Kilmore.
The following routes have no service: 4, 13, 13a, 17a, 27b, 33b, 37x, 39x, 39b, 40, 40a, 40b, 40c, 40d, 70x, 83, 102, 105, 127, 129, 142, 230, 237, 238, 239.
The following routes have a limited service: 27x, 37, 38/a, 38c, 39, 41, 41c, 41x, 43, 70/a, 270.