Sheikha Hamda al-Nahyan and her seven daughters, who are relatives of UAE President Sheikh Khalifa bin Zayed, hired a floor of rooms at a luxury hotel over eight months in 2008.
They brought with them from the United Arab Emirates an entourage of more than 20 servants whom they are accused of holding in conditions close to slavery.
The case came to light when one of the servants escaped from the hotel.
One of the alleged victims told Belgian television that the women were detained in hotel rooms with private guards and prevented from going outside. They had to be available to take orders 24 hours a day, slept on the floor in the princesses’ rooms and forced to eat the princesses’ leftovers.
One who complained is alleged to have been deprived of food and water for three days.
The princesses are being tried in absentia along with an Indian butler.
If found guilty, the members of royal family could face hundreds of thousands of euros in damages and even a prison sentence. However, rights activists say it is highly unlikely that the UAE would extradite them to serve time behind bars.
As well as charges of inhumane treatment, the princesses are also accused of failing to procure the correct visas and work permits for their servants as well as failing to pay wages.
The princesses deny the charges.