Tens of thousands of commuters in Dublin are being forced onto alternative transport in the second strike on the Luas network.
Trade union leaders in Siptu said they fear the 48-hour walk-outs will continue for weeks or months after there was no contact with management or mediators in the last week.
The latest stoppage is scheduled to run until Saturday, hitting about 90,000 passengers each day.
Workers' representatives, who have been championing salary hikes of 8% to 53%, claim pay scales mean drivers can work for nine years and hit a salary of €42,247 or €47,941 for traffic supervisors.
LUAS: Services not running today due to strike. Tickets not valid on other transport providers. Expect delays. https://t.co/qvBPcgxUj8
— The AA Ireland (@aaroadwatch) February 18, 2016
Transdev, which operates Luas under a contract with the state, has pulled bonuses worth up to €750,000 for the workforce of 250 but said it remains open to pay rises, albeit closer to the 1-3% mark.
The company is facing penalties of more than €100,000 every day services do not run.
Our services are operating as normal this morning but due to Industrial Action at Luas please allow additional time for your journey.
— dublinbusnews (@dublinbusnews) February 18, 2016
Owen Reidy from SIPTU said that they never wanted it to come to this.
"We are very sorry about this," he said.
"I can assure them that the workers who have been working with this company for many years, some since the very start, would much rather be delivering the public service that they're proud to do rather than walking around the picket lines for the next two days.
"They're equally determined to get what they consider to be a just resolution to this dispute, and I think it's incumbent on all of us to sit down, roll up our sleeves and reach an agreement."
He said the workers are determined to get some form of pay rise.
"We'd happily dance with anybody but the radio studio is the only place we've had talks this week," he said.
"The workers are determined to get a just outcome and even those who would rather not be on the picket line are serious about reaching an agreement."
Transdev said the pay claims would cost the company more than €20m over five years.
Gerry Madden from Transdev claimed that Luas drivers already enjoy some of the best pay and conditions in the world.
“Owen Reidy has been invited, on numerous occasions, by myself and others, to seriously look at the claim,” he said.
“We, as an operator, Transdev, are in the business of running light rail. We’ve gone and looked at, not just in the countries where we operate but beyond that as well to find out if there’s any train drivers who earn better pay and conditions – we can’t find any.
“At the very least, I think Owen Reidy and Siptu need to explain to the massive amount of people who are going to be inconvenienced by this strike – what justification for these pay claims?”
Transport Minister Paschal Donohoe said he was powerless to offer more money to meet the demands.
A further two strikes are planned, including on St Patrick's Day.
A spokeswoman for Transdev said: "We have been saying since January that we are willing to engage on pay claims."