An Irish Congress of Trade Unions (Ictu) disputes committee has upheld a number of complaints tabled by Siptu in a row with the Unite trade union over the alleged poaching of members.
Siptu complained to Ictu last April that Unite had taken into membership a number of crane operators in the construction sector who traditionally had come within its sphere of influence.
It is understood that there were about 50 contested members between the two unions.
It is understood that the executive committee of Ictu on Wednesday accepted a report drawn up by a three-person disputes committee that recommended that Unite should terminate the membership of the crane operators and encourage them to return to Siptu.
Siptu had argued that for many decades it had the rights to negotiate on behalf of general operatives and related categories of workers in the construction sector and that crane operators were not a separate negotiating unit.
Siptu said it represented about 14,000 general operatives overall.
Unite said it had been approached by a group of crane operators earlier this year.
It said it had sought to develop a common approach between the two unions on representing crane operators.
Unite said, through a predecessor union, it represented general operatives across all sectors including construction, particularly in counties Waterford and Louth.
The inter-union row formed a backdrop to the recent strike action by crane operators over pay which disrupted a number of building sites over recent weeks.
Under the rules of Ictu,Unite has 30 days to lodge an appeal against the finding of the dispute committee.