"Many staff have been in a holding pattern for over a month, which has created uncertainty, paralysis, and low morale.
"They should also know that the manner in which Green staff have been treated has already diminished the reputation of the Green Party."
The letter also states staff were prevented from providing feedback on a proposed staffing structure and "MPs impinged upon important rights to be heard".
The Green Party has always seen itself as a champion of workers' rights and will see the leak of the letter as damaging to the party's image.
A party spokeswoman said the party did not comment on employment matters.
The Greens gained a slight boost in the latest 1 News Colmar Brunton poll, moving from 6.3 per cent support from election night to 7 per cent.