First Minister Carwyn Jones has pledged his Government will do all it can to bridge a funding gap when it takes responsibility for council tax benefit.
The UK Government has devolved council tax benefit to the Assembly, but with a 10% cut. As many as 230,000 homes in Wales would be hit with a council tax bill for the time.
AMs have been recalled from recess to vote on the regulations on December 19 after they failed to approve them last week amid a row over process.
The First Minister said: “It will be difficult to find that money in-year particularly and in the financial years to come.
“We will continue to look at the situation but it certainly isn’t easy to plug a gap that the Treasury has created.
“We will try to see what can be done to try to close that gap.”