The nurses organisation says "the good has nearly gone out of the pandemic bonus payment for healthcare staff", due to delays.
The bonus of €1,000 was announced in January as a thank you to frontline staff who worked in settings exposed to Covid-19.
The INMO reported last week that only two hospitals had paid the bonus to workers.
Director of Professional Services Tony Fitzpatrick says many nurses have yet to receive the money:
"It's absolutely ludacrious at this stage.
"It's a shambles that healthcare workers who stepped up during the pandemic never stepped back, they never thought twice.
They put themselves at risk, they put their families at risk.
"And it's now vitally important that this money is paid immediately."