Plans for a business park in the Lake District developers said would create 1,000 jobs have been refused.
Outline permission was being sought for the 15.5 hectare site at Ratherheath, near Kendal.
The Lake District National Park Authority said it was one of the biggest planning applications it had faced in recent years.
Developers The Ratherheath Partnership (TRP) said it would appeal against the decision.
Members of the park authority's development control committee refused the application.
The authority said it and South Lakeland District Council had received more than 200 objection letters.
Reasons for refusal included concerns TRP had not demonstrated a need for the site on national park land.
The firm had also not demonstrated that existing employment sites were not available and that it was hoping to build the development in open countryside, the authority added.