The National Bus and Railworkers' Union has called on Iarnród Éireann to clarify why it has forced staff to defer taking redundancy within days of their scheduled exit dates.
Last Monday, the company denied that it could not currently afford to pay redundancy lump sums of up to a maximum of €130,000 to the 17 staff in the current wave of departures.
A spokesperson said the deferral is to ensure a "phasing of funding for cash flow management."
The spokesperson also said it is "to preserve continuity of service."
Iarnród Éireann is currently implementing an agreed cost reduction programme.
450 redundancies are being sought over four years, as are significant changes in terms and conditions.
However, NBRU Assistant General Secretary Dermot O'Leary accused the company of reneging on the implementation of a vital component of the agreement over redundancies.
Mr O'Leary said the company has reneged on implementing cost-cutting measures, which were having an immediate impact on union members.
He said it did not make sense for a company seeking 450 redundancies to prevent those who applied for it from leaving.
Mr O'Leary said that the NBRU is also concerned that executives may have left the company on far more attractive exit terms than those offered to his members.
Iarnród Éireann confirmed to RTÉ News on Monday that a number of executives "in single digits" had left under a separate redundancy scheme established last year, which pre-dated the current scheme.