The Social Democrats say ESRI research proves that Budget 2020 will increase poverty rates across the country.
The party's co-leader said their analysis shows the Government has little regard for the less well-off in Irish society.
Deputy Roisin Shorthall said it is clear poverty was the last thing on Fine Gael's mind when it was planning for next year.
Ms Shortall said: "A couple, for example, on pensions will experience a cut, in effect, of around €6 a week next year. Equally, people who are on the minimum wage who are expecting a 30c increase are being denied that now.
"So, what we are saying is that people on lower incomes, who can least afford to pay, will take the brunt of Brexit, and that is completely unfair."