Representatives from the Williamtown Residents Action Group, No Sand Mine in Bobs Farm and the Hunter Koala Preservation Society have written to Federal Environment Minister Greg Hunt asking him to reject the sand mine proposals as matters of national environmental significance.

The groups say the impact on koalas in Port Stephens has the potential to leave the population in grave danger. Koalas in NSW have been listed as a nationally threatened species since 2012.

Castle Quarry Products plan to mine 4.6 million tonnes of sand at Williamtown over 15 years, while in Bobs Farm, Ammos Resource Management propose to mine 10 million tonnes on a 40-hectare site.

Ecologist David Paull said that both locations contained important koala habitats earmarked for bulldozing if the sand mines went ahead.

"These mines could mean death by a thousand cuts for the the Port koala population ... this is why we need a national approach to koala protection," Mr Paull said.

Williamtown's Cain Gorfine said Port Stephens Council's own mapping had shown that the Williamtown sand mine was located on preferred koala habitat.

"We are in disbelief that they would lease such an important ecological area out to a sand mine," Mr Gorfine said.

Barry Elliott, of No Sand Mine, said that the koala was a national icon which should not be lost to future generations.

"We are calling on Mr Hunt to reject these sand mines that put our koalas and water at risk."

Federal MPs Sharon Claydon (Newcastle) and Bob Baldwin (Paterson) have indicated that they would deliver the letter to Mr Hunt.