Average disposable income in Irish households fell by just over 3% between 2010 and 2011, according to the latest official figures.
The Survey of Income and Living Conditions found that it slipped from €22,138 in 2010 to €21,440 in 2011.
The Central Statistics Office research also reveals a significant rise in the share of the population at risk of poverty, from 14.7% in 2010 to 16.0% in 2011.
Commenting on the findings, Social Justice Ireland said the number of people in poverty has now reached a record level of 733,000.
Fr Sean Healy blamed the deterioration on decreases in Child Benefit, reductions in social welfare rates, over-taxation of the working poor and the failure to invest enough in creating jobs.
The children's charity Barnardos particularly highlighted what it called "the stark increase in deprivation rates for one-parent families to 56% in 2011".
Its Head of Advocacy, Catherine Joyce, said that some one-parent families have seen a €60 decrease in their weekly income since 2009.
The charity also underlined the increase in the rate of children in consistent poverty, from 8.8% in 2010 to 9.3% in 2011.