Train-drivers who were involved in a series of bitter disputes with Iarnród Éireann are to vote this week on a proposal that they join the National Bus and Rail Union.
The ballot follows an internal review of its options by the Irish Locomotive Drivers' Association, which disrupted train services for 10 weeks in the summer of 2000.
Mr Brendan Ogle, chairman of the committee which carried out the review, said that joining the NBRU was the "least worst option" open to ILDA's 99 members.
Alternatives considered by the review committee included joining SIPTU or remaining in the ATGWU, to which ILDA affiliated in controversial circumstances in March 2001.
Although the Irish Congress of Trade Unions instructed the ATGWU to expel ILDA, the association threatened legal action and continues to exist as a branch within that union.
The decision to ballot on joining the NBRU was taken at a general meeting of ILDA members on Sunday.
Mr Ogle said the fact that the NBRU, unlike SIPTU, was not a member of the ICTU had been a factor in the decision.
Joining SIPTU, which currently represented 199 train-drivers, would also give that union an effective monopoly position, he added. The NBRU had 56 train-drivers in its membership.
The ballot, to be concluded next week, provides for ILDA members to join the NBRU as individuals.
It would not exist as a branch, as it had done in the ATGWU, but "no definitive decision" had been taken on whether ILDA would continue to exist in some form.
To be accepted, the proposal requires a simple majority in all six of ILDA's branches.
In its review, which began in November, ILDA concluded that its continued existence as a registered trade union was no longer sustainable.
It also acknowledged that it had failed in its objective of achieving a driver-only union, representing all or even a majority of train-drivers. ILDA was established in September 1998 as a result of, the review says, drivers' demands for their own union going back many years.
Iarnród Éireann, however, refused to negotiate with the union, and it also had an extremely difficult relationship with SIPTU and with the NBRU. Both unions, however, have expressed a willingness to accept the ILDA drivers as members.