Natural Resources and Environment Minister Surasak Karnjanarat's proposal a safety fence be built around a rock platform at Pha Dieo Dai, a popular viewing point for scenic Khao Yai National Park, has run into stiff opposition.
Conservationists say such an artificial structure would devalue the World Heritage site.
Representatives of several conservation-minded groups showed up at the Ministry of Natural Resources and Environment on Monday to lodge a protest after park officials distributed a questionnaire asking visitors whether they agreed with the idea to build the fence at Pha Dieo Dai.
The questionnaire also offered four proposed designs of the fence for the tourists to choose from.
The minister, Gen Surasak, said it was his idea to build a safety fence. He feared that a careless tourist enjoying the scenery might end up plunging down the cliff.
Conservationists pointed out that no visitors had fallen from Pha Dieo Dai and said that putting up a fence would damage the natural features of the rock platform.
The minister said that park officials who scaled down the cliff had found many belongings at the bottom that tourists had dropped and lost. There was a high risk that a tourist taking a selfie could fall, Gen Surasak said. He wanted to prevent this ever happening.
Tawan Sikanil, chairman of the Rak Khao Yai Network, said construction of the fence would require the transport of bricks, gravel and sand and other material to the site. This could also damage the natural environment.
Warning signs erected at the viewing point should be enough, he added.
Instead of thinking about building a fence, the minister should issue a regulation to stop tourism in areas such as Bung Phai, Khao Laem and Khlong E-thao in the national park.
Mr Tawan said his network would oppose the proposed fence to the end.
He said renowned songs for life singer Pongthep Kradonchamnan would take to the stage in front of Khao Yai on June 5, World Environment Day, to declare his intention of protecting the World Heritage site.
If Gen Surasak insisted on building the fence, the network would petition both the minister and the National Council for Peace and Order against it, Mr Tawan said.