Bulgaria, a NATO member, is refusing to let Russian military flights fly through their airspace on their way to Syria. Makes sense to me. Let the Russkies take the long way around. They've got oil to burn.
https://news.vice.com/article/bulgaria-to-russian-military-aircraft-you-shall-not-pass
https://news.vice.com/article/bulgaria-to-russian-military-aircraft-you-shall-not-pass