People visiting or camping in national parks in NSW face hefty increases, and staff have been told to be "proactive" in the hunt for asset sales and alternative uses of their own accommodation, according to a leaked document submitted to parliamentary estimates hearings.

Park staff are urged to help secure the "financial sustainability" of the National Parks and Wildlife Service amid "ongoing budgetary pressures … and decreasing expense allocations across future years", the deputy chief executive of the service, Michael Wright, stated in a letter dated June 29 this year.

Camping and entry fees are about to rise at National Parks in NSW. Credit:David Tao

The letter lists eight "sub-projects" for savings and revenue, including "a review of assets currently deployed as staff accommodation","retention of revenue derived from asset sales", and an increase to park use and camping fees.

Mark Speakman, Minister for Office of Environment and Heritage, told Estimates on Friday entrance fees, though, hadn't increased since 2004 and those for camping since 2007, and so were due "for a catch-up".