Irish Federation of University Teachers President Marie Clarke has said trust has been broken between unions and the Government.
Addressing the IFUT conference in Dublin, she accused the Government of breaching a number of guarantees in the first Croke Park agreement.
She said her members have no reason to believe the Government will honour any current or future guarantees.
She said her union did not expect what she called a "forced negotiation" of the deal.
She said there was no negotiations and said "threats and bullying" more accurately described the process.
Minister for Communications Pat Rabbitte has admitted that the Labour Relations Commission chief Kieran Mulvey, who has been given the task of trying to break the deadlock on Croke Park II, has a difficult job.
Speaking in Dublin this afternoon, Minister Rabbitte said although it is a difficult task, the nature of industrial relations is that "sometimes the impossible can be achieved".