Luas drivers are to seek a pay increase of around 40% in line with the pay scales of Irish Rail train drivers.
The claim will be presented at the Labour Court tomorrow.
The 172 Luas drivers who belong to SIPTU currently earn a maximum of around €42,000, while around 350 Irish Rail drivers can earn up to around €60,000.
The Labour Court is unlikely to issue a recommendation tomorrow, but if the claim were to succeed, it would add €6 million a year to the operating costs for the service.
A spokesperson for operating company Transdev said the company was on course for a loss this year and could not afford the proposed increase.
Luas drivers' salaries are significantly lower than those of DART suburban or Irish Rail mainline drivers.
However, their earnings compare favorably with pay rates for the 4,000 Dublin Bus and Bus Éireann drivers.
In addition, the Luas drivers did not experience the cuts in pay and conditions suffered by CIÉ group employees during the economic crisis.
The Luas drivers also received the full 6% due under the last national wage agreement, which was never paid to CIÉ employees.
Drivers are also concerned about the introduction of the Luas cross-city service in 2017, which they fear could result in higher working hours.
Any pay deal secured by Luas drivers will be closely watched by the more substantial numbers of workers in the CIÉ group.
