Rehab Lotteries is in the High Court challenging a decision to phase out state funding for lotteries run by private charities.
It claims the abolition of the scheme by 2016 will result in a reduction of services to people with disabilities and to those who are socially disadvantaged.
The High Court has heard the Rehab Group is the largest beneficiary of a scheme to fund charity lotteries, annually receiving nearly €4m of the €6m made available.
Their lawyers say the scheme is not simply "grant aid". It was set up in 1997 to compensate private charities like Rehab who could not compete with the National Lottery.
That is because charity lotteries are subject to a weekly prize cap of €20,000, whereas the National Lottery has no such restrictions.
At present 65% of the scheme is funded by the National Lottery – the remaining 35% comes from the exchequer.
Rehab is arguing the State’s decision last year to phase out the scheme was made without notice to the charities and they say it will impact on services to those with disabilities and the socially disadvantaged.