The demolition of former government buildings in Galashiels could be delayed after evidence of bats was discovered in their attic.
Bats could halt the supermarket firm's plans for Galashiels
The site is to be flattened to make way for the new Tesco superstore currently under construction in the town.
Officials from Scottish Natural Heritage (SNH) visited the buildings on 17 May to examine the bats' habitat.
If they are found to be a rare breed, SNH could impose an order halting the demolition in order to move the nests.
Work is due to start in July when staff from the Department of Work and Pensions move out.
However, officers from SNH have now discovered evidence of bats, which are a protected species.
They want to carry out a detailed inspection of the attic area.
Tesco spokesman Nick Gellatly confirmed: "We received a phone call from SNH saying they had evidence of bats in the building.
"They will be writing to us in due course and will want a detailed inspection to be carried out which of course we are happy to comply with.
"We do not know what impact it will have on our plans at this stage."
A spokeswoman for SNH confirmed it would write to the company asking for a detailed survey to be carried out.
The discovery has been welcomed by campaigners fighting to try to save the former Scottish College of Textiles.
Tom Douglas, of Borders Heritage at Risk, said: "Tesco have tried to ride roughshod over the town and I am sure many people will not forgive them for it.
"There is huge opposition to their plans to demolish a lovely historic building but if it takes some bats to come to the rescue then so be it."
Bats are a protected species under the Wildlife and Countryside Act 1981.