Kew Gardens is at risk, after it revealed a £5m revenue shortfall and the loss of more than 100 jobs.
The Royal Botanical Gardens, a Unesco World Heritage Site, will lay off staff in a bid to overcome struggling finances.
Kew Gardens, which appointed a new director and executive board in 2012, said it could make up a third of the shortfall through self-generated income, but would need to cut about 125 roles across the gardens and Wakehurst Place in Sussex.
There are currently about 750 roles across the two sites.
Keen environmentalist Zac Goldsmith, MP for Richmond Park, highlighted the importance of the world heritage site to the Government’s environment department.
He said: “Kew Gardens is a national jewel, and it would be a tragedy if its reputation were to suffer as a result of excessive cuts.
“I have made the point in letters to Defra ministers.”
This year the botanical hotspot saw a 29 per cent surge in visitor numbers, but is still making changes to cut costs.
Concerns have been raised over how the conservation work Kew does could be affected.
Richard Pyne, a volunteer at Kew, said: “It is very worrying. There is deep expertise in many areas at Kew that we absolutely have to hold on to.
“Behind the scenes there is conservation work going on that is incredibly important to the long term success.”
A spokesman for Kew Gardens said: “We will work with staff to explore all options including schemes for voluntary exits, reduced working hours and unpaid leave, before moving onto consideration of redeployment, voluntary redundancies or, as a last resort, compulsory redundancies.
“We are working through detailed plans internally and will share more once this process is completed.
“The new executive board is leading the development of new strategies in key areas including science and the public offer, as well as strategies for growth of commercially-generated income over the coming years.”