SIPTU is expected to lodge a formal complaint with the Irish Congress of Trade Unions of "poaching" and misconduct against IMPACT. This follows the failure of the unions to resolve their dispute over who should represent Aer Lingus's 1,644 cabin crew.
Talks between the two sides adjourned last night without agreement. IMPACT claims to have 1,375 applications from SIPTU members, or well over the 80 per cent limit required by ICTU rules for the cabin crew to transfer unions.
The three general officers of SIPTU, president Mr Des Geraghty, general secretary Mr John McDonnell and vice-president Mr Jack O'Connor, are meeting this morning to decide on their next move.
Senior SIPTU sources said last night they were likely to decide on complaints against IMPACT under rule 46, which covers the transfer of membership, and rule 41, which covers actions inimical to congress or an affiliated union.
A serious rift now exists between the State's two most powerful unions.
After last night' talks IMPACT general secretary Mr Peter McLoone confirmed that "the talks concluded without an agreement. As far as we're concerned SIPTU has gone off to consider its position.
"This may well result in a complaint against us by SIPTU and, if they do, we will be responding that our actions in relation to the cabin crew have been consistent with the rules of congress." Any complaint of misconduct would be responded to "vigorously".
SIPTU Aer Lingus branch secretary Mr Tony Walsh said it had not been possible to reach agreement because "it became clear IMPACT are balloting cabin crew for industrial action contrary to the rules of congress".