A prominent Victorian philanthropic organisation is facing a strong backlash over its plans to expand a disused quarry adjacent to Arthurs Seat State Park on the Mornington Peninsula and remove about 38 hectares of native bushland.

More than 75 organisations and individuals have signed an open letter, published in Friday’s Age, calling on the Ross Trust to withdraw its plans to expand the quarry and destroy bushland that opponents say is home to koalas, wallabies, powerful owls, white-bellied sea eagles and boobook owls.

The signatories include environmental groups who have previously received funding from the Ross Trust – which makes philanthropic grants and holds $60 million in assets and investments – but have suspended their relationship over concerns about the quarry proposal.

They include the Australian Conservation Foundation, Environmental Justice Australia and the Places You Love Alliance. Another group, the Knox Environment Society, has returned a $40,000 grant in protest and donated $1000 to the community campaign opposing the new quarry.

Other signatories include former Greens leader Bob Brown, Australian Davos Connection founder Michael Roux, philanthropists Samantha and Charlie Baillieu, former CSL director Brian McNamee, Professor Will Steffen of the Climate Council, Environment Victoria, Friends of the Earth and Landcare.

A number of high-profile Mornington Peninsula tourism attractions have also signed, including the Peninsula Hot Springs, concerned about the visual effect of the quarry.

The open letter advertisement was organised by the Peninsula Preservation Group (PPG), which is leading the Save Arthurs Seat campaign.

Dr Mark Fancett, the president of the group, said the open letter showed the breadth of concern about the Ross Trust funding its philanthropic operations through a new quarry.