Update 10am: Siptu has warned the long-running Luas pay dispute could run into July and beyond.
The tram operator Transdev had warned staff that if a work-to-rule went beyond 4am today, they would reduce workers pay.
The next strike is expected on Wednesday and Siptu's Owen Reidy said there was no end in sight.
"People are angry and frustrated," he said, "by the attempt in recent days by the company to demonise the shop stewards. It has backfired."
Meanwhile Luas services are back up and running again.
A technical fault brought the Green Line to a halt for a couple of hours this morning. Luas said there may be some slight delays on services.
Luas drivers will push on with their pay claim despite the threat of a 10% cut to their wages if they continue to strike.
Drivers last night discussed the threat by Transdev to cut their pay from this morning and decided to continue with their industrial action.
Drivers downed tools for the ninth time yesterday. A further five days are scheduled for May, starting next Wednesday.
Owen Reidy from Siptu said: "There's about 3% or 3.5% between us and Transdev and it's important we try to negotiate a settlement, but the company won't talk" he said.
"The workers are very clear that they will not be humiliated. They want a negotiated settlement, but in the absence of talks they will continue with their protest and their industrial action until they get a just outcome."