The apparent destruction of slow worms on land being developed for housing has been described as "outrageous."
Tufa Field, a nature reserve in Odd Down in Bath, is being prepared for 37 new homes by contractors.
However, during work to re-home the reclusive protected species, nearby residents said a tractor pulling a plough killed several.
Bath and North East Somerset Council said it was investigating the allegation.
Slow worms have protected status in the UK and under the Wildlife and Countryside Act 1981 it is illegal to intentionally kill or injure them.
Resident David Roberts called it an "outrage", and said it had made many residents "angry and upset".
He said the council had "shown no mercy for a protected species".
A Bath and North East Somerset Council spokesman said its development company had commissioned some preliminary ecological works on the site.
"These include the trapping and relocation of the reptiles to a safe area of the site," he said.
"We would expect all developers to abide by the rules and the council will take appropriate action where they don't.
"We are aware of the concerns raised on social media about the protection of wildlife on the site and we are investigating the specific issues raised."
Avon and Somerset Police said the matter had been reported to the force and officers were liaising with the council.
Although they resemble small snakes, slow worms, which are a protected species, can be more accurately described as lizards with no legs.
Measuring up to 50cm, they can live for 20 years and are found in most of the United Kingdom.
They have smooth skin and the best time to see them is between May and October, after which they hibernate.