The party's public sector policy, released on Thursday, also commits to ditching the Coalition's cap on government staffing, and replacing it with a cap on consultants and contractors instead.

It will also seek to enshrine in law public servants' right to express political views; a right that is currently being tested in the High Court.

Greens leader Richard Di Natale said the Australian Public Service had been "privatised by stealth" since Tony Abbott's election victory in 2013.

"Job cuts by successive governments have hollowed out government departments, creating a stronger reliance on the big four consulting firms, all of which are big donors to the major parties," he said.

The Greens aim to use their numbers in Parliament after the election to reverse recent job cuts and restore staffing to 2012-13 levels.

The latest budget papers suggest that would involve creating an extra 14,500 full-time-equivalent jobs.

The policy is effectively the opposite of the Coalition's promise to shed 12,000 public service jobs, which it made before the 2013 election and fulfilled in government.

The Greens say a consequence of that decision is "out-of-control" public spending on labour-hire and consulting firms.

It proposes to "put an end to the gravy train for consultants and contractors and put an end to the 'brain drain' from the public service to private companies".

The party believes capping spending on consultants and contractors at 7.5 per cent of each agency's budget would save $10.2 billion over a decade, which could be reinvested into the APS.

It will also seek to ban departments from using labour-hire companies, "except in exceptional circumstances, and unless approved by the minister and reported to parliament".

The Labor opposition has also committed to removing the public service's cap on staffing, and has expressed concerns about the growing use of contract labour.

However, it has not explicitly recommended increasing the bureaucracy's workforce.

The Greens' proposal for "fair pay" in the APS involves increases of 4 per cent a year over the next four years. It says this will "help spark an increase in wages across into the private sector and would send a strong message that workers in the public sector are valued and respected".

The Abbott government implemented a tough pay-bargaining policy for public servants that remains in place, capping wage rises at 2 per cent a year.

Many bureaucrats went without a pay rise for three or more years because their agencies struggled to negotiate deals that both staff and the government would sign off on.

The Greens have also pledged to abolish "efficiency dividends" - annual cuts to government agencies' operating budgets - and to increase the independence of department heads by involving Parliament in the appointment process.