Trade union SIPTU has announced 13 more days of strike action at Dublin Bus.
These will be held this month on Tuesday 27th and Wednesday 28th, in addition to the 48-hour strike already scheduled for next week.
In October, the work stoppages will take place on Saturday 1st, Wednesday 5th, Friday 7th, Monday 10th, Wednesday 12th, Friday 14th, Tuesday 18th, Wednesday 19th, Monday 24th, Wednesday 26th and Saturday 29th.
Transport Minister Shane Ross said he greatly regrets the inconvenience caused, and is "acutely aware" of calls for him to directly intervene.
However, he reiterated that "any ministerial intervention could be interpreted as a commitment to open the State chequebook", and so it would be inappropriate for him to do so.
He again called on management and the unions to engage with each other immediately.
It comes as a second 48-hour Dublin Bus strike is currently underway.
More than 400,000 commuters across the capital are facing travel disruption as a result.
No Dublin Bus routes, sightseeing tours and Airlink connections will operate Friday as a result of the dispute.
Nitelink services will not run on either Friday or Saturday morning - but will resume on Saturday night.
SIPTU says the escalation was agreed at a meeting attended by representatives from five unions at Dublin Bus.
Transport organiser Owen Reidy said: "Despite the fact that we are currently in the third day of strike action resulting from this dispute, it would seem that the management of Dublin Bus and the Department of Transport have little interest in resolving the outstanding issues.
"Our members are disappointed that the only response so far from the CEO of Dublin Bus to this dispute has been to call for talks at the Workplace Relations Commission to discuss a Labour Court recommendation that has already been rejected by over 90% of our members.
"It is not a genuine attempt to find an agreed resolution to this dispute."
"Unnecessary and unjustified"
In a statement, Dublin Bus said: "This industrial action is unnecessary and unjustified and will continue to cause significant disruption to our customers and trade in Dublin city.
"To date, this industrial action has cost the company in excess of €4m and continues to impact the financial stability of the company.
"We will now assess the full implications of today's announcement."
The company accepted a Labour Court recommendation of a pay hike of 8.25% over three years for all employees across the company, calling the increase "fair and reasonable".
It says the request from workers for a 15% pay increase will cost €50m over a three-year period and "seriously undermine our financial stability".
The general-secretary of the NBRU, Dermot O'Leary, said: "It is unfortunate that Dublin Bus and those responsible for providing a public transport service for the citizens of Dublin will not engage with bus workers in relation to the claim for a long overdue pay rise.
"What is particularly galling here is the undisputed fact that this dispute will ultimately be settled around the negotiating table, allowing service disruptions to become the de-facto norm in the nation’s capital is a sad indictment on those who are both elected and appointed to provide this vital service."
Newstalk Drive's Henry McKean spoke with one driver on the picket line.
