Hundreds of schools could face closure after the mid-term break when members of the country's largest second-level teaching union withdraw from supervision and substitution duties.
The Association of Secondary Teachers in Ireland (ASTI) is also planning seven days of strike action, between next week and early December, as part of its pay campaign.
It remains unclear, however, whether other teachers in dual-union schools will cross the picket line.
The Teachers' Union of Ireland (TUI) is refraining from industrial action, having struck a deal with the Department of Education last month.
So what’s the background? And why are only ASTI members at odds with the government?
Pay inequality
New teachers were hit with a 10% pay cut, as with other public service entry grades, under Fianna Fáil austerity measures in 2011.
Salaries at every scale were reduced for new entrants taken on from January of that year, with part-time hourly rates and allowances also being cut.
Qualification allowances for first-time teachers were abolished a year later as part of Budget 2012.
This was partially compensated for by allowing entrants to start on a new scale, with a higher salary than the previous starting point.
The salary imbalance began to be alleviated under the Haddington Road Agreement, which restored allowances and introduced improved pay scales for new teachers.
The Lansdowne Road Agreement extended these provisions up to September 2018.
Croke Park hours
ASTI members voted in May to withdraw from the extra 33 hours of non-teaching time introduced by the Croke Park Agreement and continued under Haddington Road.
The union had already rejected Lansdowne Road proposals that came into effect in July.
Sanctions imposed on the ASTI as a result include an increment freeze, non-payment for supervision and substitution, and the withdrawal of improved entry-level pay scales for new teachers.
The penalties, invoked under FEMPI legislation, will leave its members up to €31,000 worse off by 2020, according to the Department of Education.
On Oct 27 ASTI teachers will take strike action over pay of recently qualified teachers. Teachers explain why https://t.co/WcqY75BNhW
— ASTI (@astiunion) October 17, 2016
By contrast, thanks to a deal reached last month, recent recruits in two of the other main teaching unions will receive pay increases of up to €2,000.
The package, which includes a revised pay scale, was secured by the TUI and Irish National Teachers’ Organisation (INTO) due to their having accepted Lansdowne Road.
The government estimates that the income boost will be worth €135,000 over the course a teacher’s career.
There will be a 15% increase in the starting pay of new entrants between August 2016 and January 2018 – from €31,009 to €35,602 – when other Lansdowne Road increases are factored in.
TUI and INTO members recruited since September 2015, meanwhile, will see a 22% increase in their pay – rising to €37,723 from €31,009 – over the same period.
But none of these benefits are available to ASTI members because of their union’s repudiation of Lansdowne Road.
Looking ahead
The Department of Education has acknowledged that a pay gap of around €1,800 continues to exist between those recruited before and since January 2011.
It points out, however, that a new commission is being established to advise on pay restoration, which is expected to report back to the government in the second half of 2017.
It also insists that penalties imposed on the ASTI following its rejection of Lansdowne Road can be suspended if the union agrees to cooperate with Croke Park hours while talks are taking place.
This would allow ASTI members to receive payment for supervision and substitution, as well as other benefits and protections provided for under the agreement.
But the union has declined the offer, calling instead for the full restoration of equal pay.
The ASTI says it remains open to talks without preconditions. At this point, though, it looks unlikely that industrial action will be averted.