Luas drivers said they will strike again on 2 and 3 April, and 23 and 24 April.
Strikes are already scheduled for St Patrick’s Day, Easter Sunday and Easter Monday.
SIPTU district divisional organiser Owen Reidy said the drivers had been left with no alternative.
Managing Director of Transdev Gerry Madden said: “The public will have no tram service for St Patrick’s Day, no tram service for Easter Weekend and now no tram service for two weekends in April.
“Transdev is in talks tomorrow in the Workplace Relations Commission with three out of the four grades in the company. Luas traffic supervisors, revenue protection officers and supervisors.
“All of these grades are willing to enter talks with the company in the WRC,” Mr Madden said.
“Transdev is willing to talk with the driver grade in the WRC but have stated that those talks will only be meaningful if the pay claim is modified to a reasonable point.
Previouly 19th February
Second 48-hour Luas strike, both sides remain at loggerheads
With SIPTU describing Luas driver demands for 54% pay increases as ‘ambitious opening, both sides remain at loggerheads. At the moment there appears no prospect of talks to end the impasse, which has already led to four days of strike action. But with the two sides so far apart, sources say even experts like the Workplace Relations Commission and the Labour Court are reluctant to convene talks, as at this point it would be an exercise doomed to failure. RI, the Ibec group that represents the retail sector, expressed concern over plans for further action and particularly on 17 March. Director Thomas Burke said the prospect of such action during St Patrick’s Day, when the city is full of tourists, must be avoided.