The Council of Trade Unions says the Ministry of Social Development's drug-testing policy for beneficiaries is not being properly tested.
The pre-employment drug test policy, introduced in July last year, makes testing compulsory for some jobs.
The CTU said it should be scrapped after the ministry revealed it has no data on the amount of money saved by cutting the benefits of those who have failed the tests.
CTU president Helen Kelly said more robust scrutiny is needed.
Work and Income associate deputy chief executive Liz Jones said approximately 40% of the jobs listed with the agency require the applicants to pass a drug test.
The Beneficiary Advocacy Federation says the Government introduced the policy only because of its populist appeal and the Rotorua People's Union says it cannot be justified.