A global human rights organization says Spanish police used excessive force when they faced peaceful protesters earlier this month during a disputed independence referendum in Catalonia.

The Oct. 1 vote went ahead despite a ban by Spain’s top court. Under the country’s Constitution, only central authorities can call votes on sovereignty matters and all eligible voters in Spain, and not only inhabitants of a region, should cast a ballot.

Police used batons on non-threatening protesters and caused multiple injuries, says Human Rights Watch in a report released on Thursday.

The U.S.-based organization says its researchers interviewed victims and witnesses in three locations and reviewed images from clashes across the northeastern region.

“At such divisive times it is especially important that authorities respect human rights, including freedom of speech and assembly, and the rule of law,” said Kartik Raj, the organization’s Western Europe researcher, calling for an independent investigation into the violence.