The company's threatening legal action against the NBRU and SIPTU, after DART drivers refused to train in new staff.
The NBRU says drivers have the right to refuse to train new recruits.
But the company claims drivers are in breach of contract, and says they're involved in “unlawful activity”.
Irish Rail and the drivers unions are currently in negotiations over pay.
But Dermot O'Leary of the NBRU, says the union is not involved any co-ordination of the workers.
