A potash mine planned for the North York Moors National Park would hit tourist spending by up to £40m a year, the park's authority has said.
Sirius Minerals needs the authority's approval to build the mine head on farmland south of Whitby.
A report to the park's planning committee said the project would bring more than 1,000 jobs but predicted a 15% loss in visitor numbers.
Sirius Minerals said it would work with agencies to help boost tourism.
According to the report, a study carried out on behalf of Sirius Minerals found the mine would not adversely impact tourism.
It claimed visitors to the area were mainly attracted to Whitby and Scarborough and only enjoyed the national park as a side attraction during their drive through.
'Tranquil and wild'
But the authority said that did not appear to be based on evidence and commissioned its own research.
It found "two thirds of tourism businesses stated that a large proportion of their customers are attracted to visit specifically because of the national park".
The key reasons for visiting were "peace, tranquillity, remoteness, the natural beauty of the landscape, especially the heather moorland, and the proximity to the coast", it said.
The report said its research showed during the four-year construction of the mine there would be a 15% decrease in visitors, resulting in a loss of £40m a year in spending.
Once operational, it predicted annual visitor numbers would drop by 14%, equal to about £38m.
Chris France, director of planning for the park, said: "People come to the National Park because it is a remote, tranquil and wild area. People come here to get away from man-made intrusions and development. It's essentially what the North York Moors is about.
"The impact of a mine being developed is clearly going to affect people's perceptions. They'll say for that period of time during construction, I'm unlikely to actually visit."
Chris Fraser, chief executive of Sirius, said in full production the project could add over £1bn to the economy.
He added: "People want to come to an area with greater prosperity and better facilities and that's exactly what the project will deliver."
The report is being considered by the North York Moors National Park Authority Planning Committee on Thursday.
A decision on whether to approve the mine is expected in the summer.