The Rehab Group say support services for up to 3,000 people with disabilities are at serious risk due to underfunding.
It says unless it gets an extra €2m from the government, services at RehabCare will be forced to close.
The group is meeting with the Health Minister Simon Harris later today in a final bid to secure the funding.
Ms O'Meara said rising costs are to blame.
She highlighted "the cost of insurance, which this year is costing the Rehab Group almost €2m.
"Also the rising cost of meeting our obligations under HIQA, our compliance and our governance requirements... And we're happy to do that but it comes at a cost."
Ms O'Meara also highlighted "the rising cost" of staff and services as issues.
She said they hope a resolution can be found at a meeting with Mr Harris.
"We're hopeful that today, and indeed the Minister himself has said that he is hopeful, we can come to a resolution, said Ms O'Meara.
"But there is no doubt - this is our third meeting - that today is the final meeting. Today it's crunch time.
"And we have to come to that agreement today.
"So I'm hopeful, on behalf of all the people using our services - their families, our staff and all those communities right across Ireland - that we will reach that resolution today."