Luas staff have been refused a meeting with the Transport Minister, Paschal Donohoe, while further strike action is looming.
Siptu wrote to Mr Donohoe earlier this week asking for a meeting to brief him on their concerns about the ongoing industrial action at the light rail company.
However, in his reply the Minister said it would be "inappropriate" for him to meet union representatives in advance of a resolution to the dispute.
Luas operator Transdev has been meeting non-driver grades over the last few days and talks with drivers are scheduled for next Monday.
Further strike days are planned for May and June.