A world-wide appeal is planned to rescue plans for a new building to replace the cafe on top of Snowdon once labelled a "slum" by Prince Charles.
The much-criticised current café will be demolished
The building at the summit is nearly 70 years old and deteriorating, but around £2m of the money needed from private investors is in doubt.
On Wednesday, Snowdonia National Park Authority said it had until the end of June to find the money.
If they do not secure funding, the whole financial package collapses.
Authority planners gave their approval more than a year ago for a stone and glass building, designed to placate conservationists and blend in with the scenery, replacing the existing concrete block housing the cafe and mountain railway station.
It is estimated that 350,000 visitors make the trek to the top of Wales' highest mountain every year by train or on foot.
Planners agreed to the glass and stone redevelopment last year
Chief executive Aneurin Phillips told a meeting of the park authority public expectations for the project were high.
"The shortfall of up to £2m, which is expected to come mainly from the private sector, has to be raised very quickly.
"Unfortunately, we are a very small authority and this ambitious scheme is an enormous challenge for us.," he said.
"The Welsh assembly government has very kindly contributed £3 million towards the project and we are extremely grateful for their contribution.
"However, what we urgently need now are contributions from the private sector.
"We have come so far and achieved so much it would be a tremendous shame to fall short at the final hurdle."
He added: "The summit of Snowdon deserves a building which the whole of the Welsh nation should be proud of."
Previous efforts to redevelop the cafe - built in 1935 by Sir Clough Williams-Ellis, the creator of the tourist Italianate village of Portmeirion on the north Wales coast - have all stalled because of a lack of cash.
Work on the latest scheme had been expected to be complete by June 2007. Now its feared that that it will too fail.
Last October Environment Minister Carwyn Jones confirmed a £3m injection from the assembly government.
More than £1m had also been secured by grants from the Wales Tourist Board, Welsh Development Agency and Snowdon Mountain Railway.
'Pinnacle of tourism'
Financial advisers have said it will be difficult to raise even half the £2m needed.
Rob Owen from the Snowdonia Society, a charity set up to protect the area, said it was important the new cafe was built.
He added: "It's essential for tourism and development of all sorts in north Wales and Wales as a whole that Snowdon, the pinnacle of Welsh tourism is presented in the best possible way to the people who will see it.
"There are all sorts of reasons why things couldn't happen in the time they should have done."