The Communications Workers Union (CWU) is meeting at Government Buildings this morning to formally complain about An Post's planned closure of the SDS parcel delivery service.
The CWU is citing An Post for breaches of the national partnership agreement, including failure to consult workers prior to its decision to close the service.
CWU general secretary Mr Steve Fitzpatrick is formally conveying his union's complaint before a special sitting of the National Implementation Body at the Department of the Taoiseach.
The union has the support of the Irish Congress of Trade Unions.
Mr Fitzpatrick, earlier condemned An Post for what he said was "the total betrayal of the 800 committed workers at the SDS service".
He also accused An Post management of a deliberate and premeditated attack on the current talks at the Labour Relations Commission on the transformation of the national postal service.
The CWU will issue a statement following the hearing.