Australian Taxation Office staff will vote on management's proposed enterprise agreement between June 27 and June 30.
The Community and Public Sector Union and the Australian Services Union have balloted their tax office members. In each case, the vast majority has voted to reject management's offer.
The two unions have agreed on a joint campaign to reject management's draft agreement.
They have produced joint posters and leaflets pointing out that management's pay offer of 9% over three years is likely to be less than the rise in the cost of living over that period.
The production of joint campaign material is a remarkable turnaround, given the long history of antagonism between the two unions.
In 2009, the Australian Services Union did a separate deal with the tax office, resulting in an agreement the Community and Public Sector Union considered very inadequate.