SIPTU Vice President Patricia King has warned that the union will not sign up to a new public service agreement if it involves compulsory redundancies.
Ms King said trade unions exist to represent the best interests of their members - and recommending that they be sacked was not in their best interests.
She said opposition to compulsory redundancies was a fundamental trade union position in both the public and private sectors.
Ms King was speaking as she arrived for talks on a successor to the Croke Park Agreement.
Management representatives declined to comment.
The talks are focused on scheduling detailed negotiations over the coming weeks with a deadline of the end of February for a deal.
The Government is demanding an additional €1 billion in savings between 2013 and 2015 - over and above reductions planned under the current agreement.
Minister for Public Expenditure and Reform Brendan Howlin said a time frame for talks on an extension to the Croke Park Agreement will be set out today.
Speaking on his way into Cabinet this morning, Mr Howlin said reaching a deal will not be an easy task.
He added that the timeframe would have to be tight.
Following a plenary meeting yesterday, unions said the Government's initial proposals were so severe that they would not be accepted by members.
Tánaiste Eamon Gilmore said it was not surprising that there was disagreement at the beginning of the talks.
Mr Gilmore refused to put a timeframe on the talks, but said it was important a deal was reached.
The Labour Relations Commission team that brokered the original Croke Park Agreement faces an uphill task in trying to find a middle ground between public service management and unions.
The Government has tabled far-reaching proposals ranging from pay cuts for higher grades, to working longer hours for the same pay, to reductions in premium pay.
Rosters, increments, more flexible redeployment, and performance based contracts for management grades are also to be discussed.
Staff representatives insist the core Croke Park protections from pay cuts and compulsory redundancies must remain in place.
They stress they have not accepted any management proposals, and that any outcome must be necessary, fair and capable of passing in a union ballot.