Luas employees have escalated their pay dispute by serving strike notice for a further six days later this month and in May.
The workers have already been on strike for eight days: four days in February, Easter Sunday and Easter Monday in March, and 3 and 4 April.
A further 48-hour stoppage has been scheduled for 23 and 24 April.
However, this evening SIPTU served notice of industrial action on Luas operator Transdev, notifying the company that there will be strikes on 28 April, 4 May, 13 May, 20 May, 26 May and 27 May.
All of the strikes will be 24-hour stoppages, with the exception of the 26 May which will only last four hours.
Transdev Managing Director Gerry Madden accused SIPTU of blatant disregard for the travelling public.
He said the company cannot stand still while its already challenging financial position is further eroded.
It is now taking legal advice about what courses of action are open to it.
The dispute originally centred on claims for pay increases of up to 53% over a number of years.
After marathon talks at the Workplace Relations Commission, a set of proposals was hammered out involving phased pay increases totalling 10% over 33 months, with an additional long service increment for longer-serving staff resulting in total increases of up to 18%.
However, those proposals were almost unanimously rejected because the increases were deemed insufficient.
Staff also objected to productivity concessions that would be required, and lower pay rates for new entrants.
Transdev subsequently indicated that the WRC proposals were off the table and no additional money would be made available to improve the offer.
Gerry Madden, Managing Director of Transdev, said the strike notice "shows a continuing blatant disregard by SIPTU for Luas customers and the travelling public".
He added the strikes were designed to cause "maximum customer disruption".
Mr Madden said that as SIPTU has served notice of strike action but has not engaged or sought to engage in any talks with Transdev, the company will take legal action on what courses of action are open to it.
SIPTU Divisional Organiser Owen Reidy said in the absence of an agreement, or any prospect of an agreement, the workers had no alternative to serve notice and continue with industrial action.
Mr Reidy said there was now a window of two and a half weeks to resolve the dispute before further stoppages.
He said the company had to consider the three reasons why the workers had rejected the WRC proposals and come to the table with fresh thinking.
He also noted that SIPTU had given notice way in excess of requirements under their collective agreement in order to create a space for talks.
