The possibility of school closures this autumn as a result of strike action by teachers has grown after the ASTI teachers' union decided to ballot members on industrial action.
The union represents 18,000 teachers - more than half of all second-level teachers.
Meeting in Dublin today, its Central Executive Committee agreed to hold ballots for industrial action over two separate issues.
The ASTI will ballot its members on industrial action - up to and including strike action - on the issue of pay for newly qualified teachers.
It will simultaneously ballot members on withdrawal from supervision and substitution duties.
In both instances the ASTI is recommending that members vote in favour of industrial action.
At its annual conference earlier this year, ASTI delegates agreed to ballot for industrial action if pay levels for new entrant teachers had not been restored by 31 August.
"Teachers who entered the profession after 2010 are on different pay scales than their colleagues even though they have the same duties and responsibilities," the union said in a statement this afternoon.
Pay levels have not been restored and so the union's central executive committee decided today to approve that earlier decision.
ASTI General Secretary Kieran Christie said: "New and recently qualified teachers are not only faced with years of casual short-term contracts, but an inferior rate of pay for doing the exact same work as their colleagues. Our goal is simple: we want equal pay for equal work."
The Minister for Education Richard Bruton expressed his disappointment at the ASTI decision this evening.
A statement said: "It is regrettable that ASTI seem determined to pursue a route of confrontation rather than dialogue."
Mr Bruton also emphasised that his Department remains available to meet with ASTI to discuss their issues of concern, including issues relating to new entrant pay.
Substitution and supervision payments were suspended for all teachers for a number of years under the now expired Haddington Road Agreement.
The ASTI believes its members are now entitled, along with members of other teacher unions, to a restoration of these payments.
However, the Government said the union must be part of the Lansdowne Road Agreement in order to benefit from restoration.
The ASTI is not party to the LRA.
The results of the ballot will be known on 14 October.
The union must give two weeks’ notice before any industrial action takes place.
The Government is proceeding with restoration of substitution and supervision payments for members of the INTO and TUI teacher unions.
The first tranche of supervision and substitution payments will appear in paychecks issued later this month. However, ASTI members will not receive the increases.