Next week's bus strike could affect Dublin Bus and Irish Rail services.
Other members of the CIE group could refuse to pass pickets when Bus Eireann strike on Monday.
Dublin Bus and Irish Rail share depots with Bus Eireann.
The NBRU say Dublin Bus are considering moving some of their buses from the Bus Eireann Broadstone depot to other depots in the city.
"I wrote to Dublin Bus yesterday and I did advise them ... that i accept that they need to do what they have to do in terms of their own business", said Dermot O'Leary of the NBRU.
"I'm just highlighting the fact ... that there's anger among the CIE workers in general".