Western Isles Council will only allow Stephanie Noble to keep the pony on condition that every door she uses, including the front, must be at least 4ft wide.
Grey Lady Too, a three-year-old dapple grey, has lived with Mrs Noble since she was left without grazing land following a dispute over a field.
Her owner has put in a hay bed and turned her chairs into feeding troughs to accommodate the animal.
She passes through four doors to go in and out of the house from inside her stable in the front living room.
The council is insisting the horse must have clearance above its head while in the living room at the home in Back on Lewis. Mrs Noble, who has received an animal care notice, said she will fight the move.