The Education Authority has apologised after a number of substitute teachers were left unpaid following the introduction of a new online register.
Trade union representatives have called for immediate financial assistance to be provided to those affected as they now face a wait until mid-October for payment.
The Education Authority (EA) has said they could not identify a "viable option" to provide unpaid teachers with an interim payment option.
The Northern Ireland Substitute Teacher Register (NISTR) was launched in August and currently includes details of approximately 7,000 teachers.
It is described as an online platform, which provides a real-time booking system and a centralised database for all supply teachers in Northern Ireland.
The EA has explained that teachers may have been left unpaid because bookings were not confirmed or signed-off prior to the payroll cut-off.
NASUWT official Justin McCamphill said the trade union is being “inundated with messages on a daily basis in relation to problems with the introduction of the new system" and has called on the EA to provide immediate financial assistance.
He continued: "Many substitute teachers were expecting to be paid today for work carried out in August.
"Failure to pay these teachers is causing extreme financial hardship in the middle of the cost-of-living crisis. Teachers have told the NASUWT that they cannot afford to put fuel in their car to get to work in the first place."
Mr McCamphill added: "It is now incumbent on the Education Authority to put arrangements in place to immediately pay a cash advance to all those impacted by the situation."
A spokesperson for the Education Authority (EA) said: “The delay to the launch of the new Northern Ireland Supply Teacher Register (NISTR) to the 29 August and the technical issues experienced in the first few days have been disappointing and frustrating for all involved.
"The Education Authority has apologised to all users for the inconvenience caused.
They continued: "Nearly 3,500 temporary teachers received salary payment for August days today (16 September) however it is regrettable that a number of teachers who worked in August did not receive payment for various reasons including bookings that were not confirmed or signed-off prior to payroll cut-off and technical access issues.
"Every potential avenue has been explored to provide those affected with an interim payment option, however unfortunately no viable option could be identified.
"These teachers will receive payment as part of the next monthly payroll run."
The spokesperson added: "The NISTR Support Team and the system suppliers and developers are working diligently to resolve any known issues."
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