Social Development Minister Paula Bennett is defending the proposed drug-testing of beneficiaries, saying she has all the evidence she needs to justify it.
Under the changes, people who fail drug tests while they are looking for work would face losing their benefit.
The Council of Trade Unions unsuccessfully tried to get official documents on employer complaints about beneficiaries failing drug tests.
CTU president Helen Kelly says such complaints were supposedly the Government's catalyst for change and the information vacuum isn't good enough.
But Ms Bennett says she has plenty of information from face-to-face meetings with employers and others, and has no time to trawl through evidence.
She says the overhaul is a "no-brainer" and just because her advice hasn't come from the Ministry of Social Development doesn't mean it's not credible.
"It's not overly complex and I just can't see how you can question whether there's a problem or not."
Labour's social development spokesperson Jacinda Ardern says acting only on sector advice is not enough.
Ms Adern says the views of those working on the front line should be tested with officials and advice sought from experts on the area.
"One such group would be the Ministry of Health. My understanding is that they do have a view on this policy and it's not a particularly positive one, but that's not information we can get the Government to release."