Department of Conservation staff are making a statement on Wednesday by refusing to do extra work not detailed in their contracts.

MORE: Consequences warned if DOC underfunding continues

1500 Department of Conservation staff will be taking industrial action by not doing over-time, answering phones or emails.

The move comes after the latest offer from DOC was rejected by 95 percent of union members.

Public Service Association National Secretary Erin Polaczuk said workers feel the whole department is under-funded, and the results of negotiations a couple years ago made little difference.

"Almost half of them didn't get any pay rise whatsoever and they've had enough. They feel undervalued, they feel that the work of DOC is undervalued by the Government, and they feel really passionately about their work and think that they're worth more."

Polaczuk said conservation on the cheap only ends up hurting endangered species and vast forests that DOC staff work so hard to protect.