Greens councillor Jill Merrin has submitted the motion for tonight's meeting, moving that the council urgently write to NSW Environment Minister Robyn Parker requesting the government buy the land.

The request comes ahead of an auction for the Lady Carrington Road property on Saturday.

The site, advertised as Otford Valley Farm, comprises almost 360 hectares of bushland next to the Royal National Park.

Much of the land is zoned for environmental conservation and Cr Merrin said it should be considered a vital addition to the park.

"The bushland area acts as a green corridor linking the national park to the escarpment and areas of reserve," she said.

"The state government planned to purchase the land in 1975, with an apparent administrative error allowing it to fall into private ownership, as stated by then MP Ian McManus.

"The state government recently purchased land to the north of this land to include in the park, and it should purchase this land too.

"I want to bring this matter to the public's attention and I know there's strong support for including this land in the national park from Wildlife Services, the National Parks Association and many people in the Illawarra."

Yesterday, Cr Merrin was confident her fellow councillors would support the motion, saying they had previously agreed to seek government support for the park to be included on the world heritage list.

She said the bushland was home to several threatened species and consisted of key natural environment identified by the Illawarra Regional Strategy.