ISTANBUL (AP) — The European Court of Human Rights on Tuesday ruled that the rights of a Turkish teacher convicted of what prosecutors called terrorism offences had been violated because the case was largely based on his use of a phone app.

The court said its ruling could apply to thousands of people convicted following an attempted coup in Turkey in 2016 after the prosecution presented use of the ByLock encrypted messaging app as evidence of a crime.

Ankara has blamed the coup on the followers of U.S.-based cleric Fethullah Gulen, a former ally of President Recep Tayyip Erdogan. Turkey has listed Gulen’s movement as a terrorist organization known as FETO. Gulen denies any involvement in the failed putsch.

Yuksel Yalcinkaya was among tens of thousands arrested following the coup attempt in July 2016, in which 251 people were killed as pro-coup elements of the military fired at crowds and bombed state buildings. Around 35 people who allegedly participated in the plot also were killed.

Yalcinkaya, from Kayseri province in central Anatolia, was convicted of membership of a terrorist organization in March 2017 and sentenced to more than six years’ imprisonment.

The European court found the “decisive evidence” for his conviction was the alleged use of ByLock, which is said to have been used exclusively by Gulen supporters.

In its judgement, the court found the case had violated the European Convention on Human Rights, namely the right to a fair trial, the right to freedom of assembly and association and the right of no punishment without law.

In a statement, the court said that “such a uniform and global approach by the Turkish judiciary vis-a-vis the ByLock evidence departed from the requirements laid down in national law” and contravened the convention’s “safeguards against arbitrary prosecution, conviction and punishment.”

It added: “There are currently approximately 8,500 applications on the court’s docket involving similar complaints … and, given that the authorities had identified around 100,000 ByLock users, many more might potentially be lodged.”

The court also called on Turkey to address “systemic problems, notably with regard to the Turkish judiciary’s approach to ByLock evidence.”

Responding to the ruling, Turkish Justice Minister Yilmaz Tunc said it was “unacceptable for the ECHR to exceed its authority and give a verdict of violation by examining the evidence on a case in which our judicial authorities at all levels … deem the evidence sufficient.”

He also protested the court’s acceptance of Yalcinkaya’s legal representative, who Tunc said was subject to arrest warrants for FETO membership.

Turkey was ordered to pay 15,000 euros ($15,880) in costs and expenses.