A union representing some ambulance workers is criticising what it calls another union's inability to come to a compromise with St John over its collective agreement.
About 1000 ambulance officers in several parts of the country have been taking strike action over the past few months.
St John has since pulled out of bargaining with the union altogether.
The Ambulance Association, which represents about 300 workers, has settled its own agreement with St John.
Its chair, Mark Quin, said First Union would not budge on its demands for a 2 percent pay rise and additional leave.
"My understanding of the situation is that First Union has made a statement and are not prepared to negotiate off those points, and as it does with any negotiation process there's got to be some room to move."
He said he hoped St John would return to the bargaining table, and that First Union would agree to a compromise.
Meanwhile, the Labour Party is accusing the government of failing to invest in the health sector.
The party's health spokesperson Annette King said the stand-off was evidence of growing industrial turmoil in the health sector caused by years of underfunding.
She said health workers were suffering because there was not enough money, and that urgently needed to change.