East Devon District Council granted consent last month, despite hundreds of residents campaigning in support of a rival Sainsbury's application (Planning, 25 September, p5).
The challenge rests on Tesco's plans to prepare the flood plain site for construction. It needs permission for an infill process, which would involve bringing in material by sea.
Seaton chairman Sandra Semple said details of the process should have been assessed before consent was awarded. "We would like a clear environmental impact assessment," she declared.
But East Devon's development manager Steve Belli insisted that a condition has been imposed to prevent Tesco starting infill work before securing permission and an assessment will form part of the application. "There are no grounds for a legal challenge," he added.