Campaign groups have warned that UNESCO could take away Stonehenge's World Heritage status if the Government goes ahead with digging a tunnel under the sacred tourist attraction.
SEE ALSO: Stonehenge tunnel gets the go-ahead
SEE ALSO: Barack Obama visits Stonehenge
The Government wants to build a 1.8-mile-long tunnel underneath Stonehenge, which it argues would be deep enough not to damage the site.
But archaeologists and campaign groups believe that it will "inject enormous amounts of concrete into the most significant prehistoric landscape" in Britain.
Members of the National Trust, which supports the plan for the tunnel, are urging it not to back the controversial plan.
Kate Fielden, vice-chairwoman of the British Archaeological Trust and a member of the anti-tunnel campaign group, the Stonehenge Alliance, told the Daily Telegraph: "As members of the National Trust our hope is to somehow persuade the Trust to change its mind.
"We think the Trust should be going for the very best for a World Heritage Site, sticking to its basic principles and seeking a better solution."
Meanwhile, UNESCO has warned the Government that the development would cause "considerable damage," while its Chief of Europe and North America, Isabelle Anatole-Gabriel, told Sky News: "We are not there, we have to assess first what are the potential impacts of any changes which might occur on the values of the site and on its integrity."