A councillor claims many local people welcome the airport
Opponents of a plan for a commercial airport in Snowdonia are considering legal action to try to halt it.
Snowdonia Society director Alun Pugh says it will seriously consider asking for a judicial review.
Mr Pugh, a former culture minister, claims the Welsh Assembly Government has not produced evidence it has met all its legal requirements.
The assembly government has asked him to be more specific in his information requests and offered to meet him.
The three Welsh national park societies have joined forces against the scheme for the former military airfield at Llanbedr near Harlech, Gwynedd.
The Snowdonia Society, Brecon Beacons Park Society and Friends of Pembrokeshire National Park all oppose the proposal on the grounds that it would damage the local environment and economy.
We're greatly concerned that Welsh ministers have not behaved in a fully lawful manner here
Alun Pugh, Snowdonia Society
Mr Pugh told The Politics Show Wales he had not seen evidence that the assembly government had met special planning requirements for national parks under the Environment Act.
"If they've met their obligations then they would have produced the evidence," said Mr Pugh.
"We've made several requests using freedom of information legislation to the Welsh government and yet that evidence has not been forthcoming. And it makes you wonder why that evidence has not been forthcoming.
"We're greatly concerned that Welsh ministers have not behaved in a fully lawful manner here."
Mr Pugh said a judicial review was "expensive and long drawn-out", and "the option of last resort".
But he said that "if the evidence is not made forthcoming that the government has indeed fulfilled its legal obligations, well, that's something that we have to consider very seriously indeed."
David Young, of Kemble Air Services, which will take over the airfield on a 125-year assembly government lease, said the dispute was "almost irrelevant from our point of view".
Mr Young said the argument between Mr Pugh and the assembly government was nothing to do with the company.
But he was disappointed with what he saw as unfair adverse publicity generated by Mr Pugh's claims.
We certainly won't have aeroplanes going from Llanbedr and flying through the mountains all the time
David Young, Kemble Air Services
The company said it hoped to create more than 30 or 40 jobs by letting building on the site, and envisaged it being used by small private aeroplanes and microlight aircraft, as well as scope to test unmanned aerial vehicles.
Llandebr is not licensed for passenger flights, and the company said it viewed any such development as an expensive goal which could perhaps be pursued in the longer term in co-operation with the local community.
"We certainly won't have aeroplanes going from Llanbedr and flying through the mountains all the time," said Mr Young.
He said the area was one of "intense aerial activity" as a training area for the RAF.
Mr Young said a newspaper description of "the drone of bumblebees having been the only sound in the Welsh mountains for decades, to be suddenly spoilt by aeroplanes coming from Llanbedr airfield" was "complete and utter poppycock."
As assembly government spokesman said it had offered to meet Mr Pugh to explain how it had met all obligations.
The assembly government has also said the plan would have "minimal environmental impact" with the emphasis on its "sustainable development in sympathy with the local area and community," while all relevant bodies had been kept aware of the development.
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