Fianna Fáil leader Micheál Martin has said the Government seemed to be targeting autism in its review of the Domiciliary Care Allowance.
Mr Martin told the Dáil that about 50% of children with autism have lost the allowance.
Speaking during Leaders' Questions, Mr Martin said the letters sent to parents are unsympathetic.
Taoiseach Enda Kenny said a report into the allowance has been commissioned.
He said the Government wanted the best possible range of supports in place for children.
Mr Kenny said it was a case of looking continuously at what are the best supports.
Mr Martin said the Government was out of touch with the issue. He said there was a deliberate policy to divest those with autism of the allowance.
The Taoiseach said he rejected the charge that the Government was targeting those with autism.
He said there was an evaluation process for every allowance.
Earlier, over 150 parents and their disabled children marched to the Dáil to protest against the loss of their Domiciliary Care Allowance.
The protesters, who came from all over the country, say the payment, along with other means-tested allowances that accompany it, can be worth some €15,000 a year to families on low incomes.
They were accompanied by Richard Boyd Barrett of the United Left Alliance and were met at Leinster House by Mr Martin.
Both men supported the group's request for an urgent meeting with Minister for Social Protection Joan Burton.