Dublin commuters are facing four days of Luas strikes next month.
SIPTU members have served 21 days notice of action on the company amid a dispute over pay and conditions.
Transdev says some tram drivers are seeking pay increases of up to 54% as part of the row - which it is not in a position to pay.
Workers are due to down tools in two 48-hour work stoppages - on the 11th, 12th, 18th and 19th February.
SIPTU Utilities and Construction Division Organiser, Owen Reidy, said, "the workers are conscious of the inconvenience these stoppages will have on their customers but believe they have no option but to conduct this industrial action.
“Rather than enter into serious negotiations the management of Transdev today decided to release a statement to the media that attempts to demonise LUAS workers. In this statement, the company ignores a number of key facts including its refusal to offer any pay increase above the CPI [Consumer Price Index] rate," he added.
Transdev Managing Director, Gerry Madden, said in the statement that "we believe the pay and terms and conditions of Luas employees are, and always have been, very favourable. Employee turnover in 2015 was only 2% and half of this was due to retirements".
99% of SIPTU members at the Dublin-based tram company gave their backing to strike and work to rule.
