The Government has come under intensifying pressure to reverse shock moves to scrap mobility grants for the disabled.
Opposition parties have described the decision that affects around 5,000 people as scandalous and reprehensible, and have demanded an immediate U-turn.
But Taoiseach Enda Kenny insisted the schemes were illegal, obsolete and discriminatory, and needed to be replaced with a fairer and more appropriate regime.
"These two schemes - the motorised transport grant and the mobility allowance - are illegal, are not in conformity with the Disability Act, are not in conformity with the Equal Status Act, and are not in conformity with our constitution," Mr Kenny said.
"We cannot stand over a scheme that is obsolete, that is unfair, that is discriminatory, that is not in compliance with these acts and therefore we have got to deal with it."
Ombudsman Emily O'Reilly had ruled last year that the scheme as it stood was illegal as it was not open to over 65s. She asked for it to be expanded.
The Department of Health accepted the scheme breached equality laws but said it could not afford the 300 million euro (£259.5 million) to widen eligibility.
Ms O'Reilly publicly criticised Health Minister Dr James Reilly at an Oireachtas committee for refusing to act on her ruling and widen the allowance.
Meanwhile, Age Action warned scrapping the schemes would have a huge impact on thousands of low-income people who depend on them.
Spokesman for the charity Eamon Timmins said the Government must have a replacement allowance lined up for after the last payments are made, saying: "Failure to have a replacement scheme agreed within four months will result in severe financial hardship 10,000 people with a disability, and this is totally unacceptable."