UPDATED 11.33am: Newly released papers show Treasury's been lobbying the Government for a long time to implement a capital gains tax.

Documents made public under the Official Information Act show that as far back as four years ago Treasury's view was that a capital gains and/or a land tax be introduced to reduce biases in favour of housing investment.

The papers show the department tendered similar advice in 2012, 2013 and again last year.

Treasury, like the Inland Revenue department, has told the Government a capital gains tax would make the tax system more progressive.

It's also advised the tax would help reduce property prices.

Other papers show Treasury's been a constant opponent to increases being made in the minimum wage.

The department's opposed proposed increases over the past two years and argued on each occasion that there was a case for the minimum wage not being lifted.

Treasury's advice has been to hold the minimum wage - saying that would deliver a cost reduction for businesses.

It's also argued the minimum wage in New Zealand has grown at a faster rate than median and average wages over the past decade.