A court in Turkey has decided to keep philanthropist and art patron Osman Kavala behind bars despite a warning from the European Council—the 47-member bloc that upholds human rights—that it would start proceedings against the country if he was not released. Kavala has been in prison without conviction for more than four years, accused of a selection of charges he has denied, which stem from funding anti-government protests in 2013 to organizing an attempted coup in 2016 for which hundreds of people were jailed.

“Turkey’s justifications for refusing to free Osman Kavala from prison have run out of steam,” Nils Muižnieks, Amnesty International’s Europe director, wrote in an open letter. Ambassadors from several nations including the U.S. and Germany have called for Kavala’s immediate release in line with a European court of human rights ruling in 2019.

“Turkey’s refusal to implement the binding judgment of the European Court is an unconscionable violation of Osman Kavala’s right to liberty and represents a serious threat to the integrity of the European human rights system.”

The letter goes on to call for the council to suspend Turkey’s voting rights or even membership in response to its decision.

“Osman Kavala has been arbitrarily detained in Istanbul’s high security Silivri prison as a consequence of barely disguised political persecution, for more than four years,” Muižnieks wrote, calling Kavala’s case “Kafkaesque” in that it has now been joined to cases of 51 other people, some of whom face serious criminal charges.

The Turkish businessman founded Anadolu Kultur, a nonprofit that supports cultural projects in Turkey, in 2002. But it is Kavala’s connection to billionaire George Soros’ Open Society Foundations—he founded the Turkish branch—that has been a large part of the case. Turkey’s president Recep Tayyip Erdoğan has accused Soros of being involved in the 2016 coup.

Erdoğan has shown no signs of contrition and after representatives in Turkey from France, Germany, the U.S., the Netherlands, Denmark, Sweden, Finland, Norway and New Zealand singed a letter asking for Kavala’s release, declared them all “persona non grata,” one step from expelling them from the country.