Minister for Education Joe McHugh has acknowledged that financial penalties imposed on ASTI members as a result of industrial action they took two years ago is "an issue".
Speaking at the TUI annual conference in Killarney he said the penalties amounted to a total of €15 million in wages lost to thousands of ASTI teachers.
Joe McHugh was responding to news that the ASTI has lodged complaints with the International Labour Organisation and the European Committee of Social Rights over the fact that their members were penalised for taking strike action while members of nursing union the INMO were not.
The Minister said his Department was taking the issue very seriously and there would be constructive engagement on the matter.
The penalties were imposed under legislation known as FEMPI designed to discourage public sector unions from taking industrial action.
ASTI teachers lost increments and other payments due to them. The union took industrial action as part of its campaign for equal pay for newer entrants to the profession.
Many young teachers are still suffering from the shortfall, which amounts to between €1,000 - €2,000 annually for individual teachers, because they continue to lag behind in terms of salary increments.
The Minister also confirmed that a statement earlier this week from the Department of Public Expenditure and Reform on pay inequality relates only to the pay of teachers employed on lower salaries between 2011 and 2014.
He said it did not include addressing the loss of additional payments for Masters qualifications, which is a cut that affected mainly second level teachers.
Joe McHugh said this issue was with a separate body, the Teachers' Conciliation Council, and had "nothing to do" with the statement from the Department of Public Expenditure and Reform.
That statement, which acknowledged "outstanding issues" on pay, was strongly welcomed by primary teacher union the INTO.
However, second level unions, the TUI and the ASTI, reacted more cautiously.
Referring to those teachers employed on lower pay between 2011 and 2014 he reiterated that whether it was through a pay review or the next round of pay talks he wanted to see the Government commitment to dealing with the issue delivered on.
Meanwhile, the Teachers' Union of Ireland is to ballot members to renew its mandate for industrial action in the event that pay equality is not achieved for its members.
At the union's annual conference in Killarney delegates agreed to ballot members by next September on action, up to and including industrial action, in pursuit of pay equality.
This is a renewing of an existing mandate that was secured from members two years ago.
ASTI considering its 'legal options'
Speaking at the ASTI Annual Conference in Wexford earlier, the ASTI General Secretary Kieran Christie said that while teachers had suffered an increment freeze and other losses - some of which were still placing them at a disadvantage three years later - it was now clear that the Government had not resorted to similar tactics against nurses and midwives who took three days of strike action earlier this year.
He said that no union should be subjected to such draconian or invidious financial emergency legislation (FEMPI), but he said it was now clear that far from the legislation being applied to the ASTI in an equitable manner, it was used in a singularly punitive and targeted way.
The union is now considering legal options, including judicial review of the original decision to penalise ASTI members, an action for breach of the ASTI members' constitutional right to equality, or a breach of contract action.
ASTI may also ask the courts to quash the original decision on the basis that the decision to allow the INMO to remain within the terms of the 2018 agreement, despite engaging in industrial action, means that the ASTI now has a legitimate expectation that the same outcome will pertain to them.
Mr Christie told delegates that in the current situation, any public sector union that might decide to undertake industrial action tomorrow has no certainty about how they might be treated, and added that the very viability of unions and they modus operandi was being challenged.
He said there was now an unanswerable case that ASTI members must be fully reimbursed for all their FEMPI-related losses over the duration of the dispute.
He also warned that the ASTI would pursue every avenue for restoration.
Mr Christie said the ASTI has written to Minister for Education and Skills Joe McHugh setting out the union's position and is awaiting a response.
He said that as matters develop, and subject to consultation with their legal advice, they will take whatever action is appropriate.
The union has also lodged a 700-page complaint with the International Labour Organisation against the Government's use of emergency legislation to restrict the trade union rights of teachers - and a further lengthy complaint to the European Committee of Social Rights.
On pay, Mr Christie told delegates that a mid-term pay review must now happen, as the PSSA has been stretched beyond its limits and now needs to be rebalanced for all public servants.
He said the pay increases in the current PSSA are "quite modest" and warned a pay rise in the next agreement is a must.
Addressing the so-called new entrant issue, Mr Christie said he would "accord some caution" to Monday's joint union-Government statement acknowledging the possibility of the issue being given consideration during any mid-term review or negotiations for the next pay agreement.
However, he said the ASTI would fully engage with the parties and explore any avenue to bring an end to pay inequality for teachers.
Mr Christie said that recent ASTI ballots had proven that the union was "a heck of a force to be reckoned with".
He went on to state: "What may be required from us all is one last push to bring this matter to conclusion. I am certain that ASTI members will not be found wanting."
Mr Christie also referred to the ASTI's complaint against sister union the Teachers Union of Ireland for accepting ASTI members during the industrial action of 2016.
At that time, a significant number of ASTI members defected to the TUI to avoid financial emergency penalties associated with participation in the ASTI industrial action.
Mr Christie said it was essential to avoid provisions that would encourage vulnerable members to engage in "union-hopping" or "union tourism" during dispute situations.
He said the ASTI complaint to ICTU stood as a strong rebuff to those, whether they be individual members or a fellow trade union, for engaging or facilitating such outcomes.
Additional reporting: Ingrid Miley