Controversial council tax benefit scheme regulations were passed by members after they were recalled to vote during recess on 19 December 2012.
Ministers hoped to get the regulations approved on 5 December 2012 at what should have been the assembly's final full meeting of the year.
But they were accused of treating the assembly with contempt by tabling hundreds of pages of technical documents around 30 minutes before the vote took place.
The scheme is the means-tested benefit that is most widely claimed by people in Wales.
It was managed by the UK government but will fall under the jurisdiction of local councils from April 2013 onwards.
The Welsh government was again criticised by members over the issue.
Conservative AM Janet Finch Saunders said the Minister for Local Government Carl Sargeant had shown "contempt" for the assembly in his earlier attempt to rush through the regulations.
Councils would not have been able to finalise their plans for the next financial year if they had not been approved by assembly members.
Plaid Cymru AM Rhodri Glyn Thomas said the government had failed to protect the poor and most vulnerable in society.
Some 230,000 benefit claimants will pay some council tax for the first time due to the changes.
"The government, certainly for the first year, should make up for that," said Mr Thomas.
He then quoted comments from Education Minister Leighton Andrews who said earlier in the year that the government had a "moral obligation" to develop a council tax system for the benefit of the most needy.
Mr Sargeant blamed the UK Government for both the delay in implementing the regulations and for any shortfall.
He said he was concerned about the impact on the most vulnerable and claimed he and other Cabinet members had tried to raise the issue in Whitehall "but to no avail".
But Plaid Cymru AM Simon Thomas told him: "The Tories are responsible for these cuts.
"You are responsible for protecting the poorest and most vulnerable in Wales.
"You have failed to do that."
Liberal Democrat AM Peter Black said he was pleased the regulations had passed, "but this whole affair could have been avoided if the Welsh government had given assembly members sufficient time to scrutinise legislation during term time".
A clause inserted in the regulations means AMs will have an opportunity to revisit the issue before the start of the 2013-14 financial year.