(CNN) — A burden has been lifted from the shoulders of Greece's working donkey population.

The country has banned "overweight" tourists from riding the animals on the popular island of Santorini, after activists complained that they were suffering spinal injuries.

Sightseers often pay to ride donkeys up steep slopes from the shore to the island's main town, but transporting heavier travelers has taken its toll on the creatures and prompted anger from campaign groups.

People wishing to ride the donkeys will now have to weigh less than 100 kilograms (220 pounds) -- or one-fifth of the donkey's body weight.

The animals "should not be loaded with a weight excessive in size, age or physical condition," the Greek Ministry of Rural Development and Food instructed.

The travel guidelines were circulated to island regions after the department received "multiple complaints and publications on the living conditions and well being of domestic animals" over the busy summer.

Santorini has steep terrain, and donkeys are often required to travel through pathways too narrow for cars. Activists have also complained about their treatment by their owners.

Footage of overweight tourists riding the animals prompted a backlash on social media in July, and a petition calling for an end to their use as transportation received more than 100,000 signatures.

'Throwaway gesture'

Activist group The Donkey Sanctuary said on its website in June that it was "dismayed" by the conditions donkeys are kept in, before meeting with representatives from the island in August.

In addition to the weight limits, the guidelines insist that the animals are exercised once a day for at least half an hour and have a continuous supply of drinking water.

But animal rights group PETA told CNN the move is a "throwaway" gesture which "won't prevent the daily suffering that these donkey endure".

Related content Best of Greece: Beautiful places and tastiest foods

"Donkeys can still be forced to carry a person weighing 15 stone 10 pounds (100 kilograms) up more than 500 steep steps four to five times a day," said Mimi Bekhechi, PETA UK's director of international programs.