Serbian President Aleksandar Vucic and Hungarian Foreign Minister Peter Szijjártó have reacted strongly to Bulgaria’s decision to introduce new, huge transit fees of €10.2 per MW/h of natural gas passing through the Bulgarian extension of the Turkish Stream gas pipeline to Western Europe – the so-ca...
Unfortunately for the EU, Hungary is part of of block.
Regarding Serbia, if you're applying, you should behave like a perfect member. Croatia and Estonia are notoriously known to have implemented EU directive as candidates, before the directive were even voted.