Instead of means testing child payments as it promised in the Budget, the coalition has now discovered it has no option but to bring in a flat-rate reduction.
It is understood major legal obstacles arose over Finance Minister Brian Lenihan's plan to tax the benefits.
Proceeding with a 10pc flat cut in the rate will mean a drop from €166 to €150 a month for each of the first two children, and from €203 to around €180 for each subsequent child.
For a low-income familywith three children that would mean a reduction of €55 a month and would represent a substantial cut in disposable income.
The decision will further inflame anger at the Government and lead to claims that the most financially vulnerable are bearing an unequal share of the burden.
The Department of Finance last night confirmed it was aware of "legal issues" with both taxing and means-testing of child benefit payments.
However, the Irish Independent has learned the Government will be forced to abandon its plans altogether because of insurmountable legal and logistical difficulties.
Government officials have spent weeks trying to find an alternative to introducing a flat rate cut for all, but to no avail.
One problem is that the Constitution guarantees the State will support families, which is taken to mean all families alike.