Employees of the National Learning Network are to march on Monday from Liberty Hall to Fás headquarters on Baggot Street to protest over pay.
They say an increase recommended by the Labour Court in July last year has not been paid because of the failure of the network's funding agencies to meet the cost.
The National Learning Network is the training and education division of the Rehab group and has about 550 employees.
Siptu, which is organising Monday's protest, says between 350 and 400 of the workers concerned are members of the union.
It took a case to the court last year, arguing that staff were entitled to the same pay increases as those received by workers in comparable organisations.
The National Learning Network told the court it was "fully reliant" on funding from Fás and the Health Service Executive (HSE). This funding had drifted "in a negative way" for the past four years, and it had "serious funding difficulties".
The court recommended that an 8.7 per cent pay increase be implemented, with effect from March 1st last year.
Siptu organiser Joan Wisdom said that having failed to secure pay increases through the normal industrial relations procedures, network employees felt they had "no option but to launch a 'no more delay on pay' campaign".
A spokesman for the National Learning Network said it was trying to meet the terms of the Labour Court recommendation through an "ongoing process of negotiation with Fás and the HSE".