90,000 Luas passengers will have no service this Thursday and Friday as staff belonging to SIPTU are staging a two-day strike.
The workers are seeking pay rises of up to 53%.
Luas operator Transdev is advising passengers to make alternative travel arrangements.
Another two-day strike is scheduled for next week on 18 and 19 February.
Further stoppages have not been ruled out.
Meanwhile, Transdev Managing Director Gerry Madden has urged employees to challenge the approach being taken by their union representatives in pursuing the current pay claim.
Luas staff say they want parity with heavy rail drivers in Irish Rail, but Transdev, which lost €700,000 last year, says the pay claim would add €6 million a year to its payroll costs, and is unsustainable.
Talks at the Workplace Relations Commission aimed at averting the strike broke down without agreement and there is no sign of any further intervention to avoid industrial disruption for Luas passengers.
Staff commenced a work-to-rule last Saturday.
As a result of this industrial action, they have now lost their annual bonus, worth 6.5% of their salary.
In a letter to staff today, Mr Madden warned the claims submitted on behalf of the workers do not provide a credible starting base for negotiations and until those claims are reviewed, the dispute will not be resolved.
Mr Madden urges staff to "exercise your rights as Union members to question the strategy that is being pursued by your internal representatives".
He says Transdev appreciates that it can be difficult to put your hand up and question the approach that is being pursued in your name, but says that is what is required if they are to move to a resolution.
Mr Madden states: "Sensible voices have to emerge and people have to be willing to express their opinions on the course of action about to happen."
Mr Madden claims a number of staff have already approached him and members of the management team in confidence to express their concerns and he stresses the company will fully maintain that confidence.
However, he urges staff to speak to their colleagues, their internal representatives and their external SIPTU officials as between them and the company they need to jointly chart an alternative course that protects and enhances the terms and conditions of all staff in a mutually beneficial way.
He tells staff that there is a path forward to resolve this dispute within the financial constraints of the operating contract and in a way that protects and enhances terms and conditions over the lifetime of the contract.
Transdev is urging Luas passengers to check out alternative transport options on the website.
The company notes that while 7 Day, 30 Day, Monthly and Annual Luas ticket holders can find details of how to claim a refund for the strike, Luas tickets cannot be used on alternative public transport providers like Dublin Bus.
