Hundreds of trucks and cars are stuck at a key Greek-Bulgarian border crossing, after a blockade by Greek farmers was met with a retaliatory blockage by angry truck drivers on the other side.

Farmers have been blockading highways across Greece for weeks to protest a government-planned pension reform that critics say will increase social security contributions to unsustainable levels. While some blockades stop traffic for hours at a time, others do so round the clock.

Greek authorities said there were about 800 trucks and about 160 cars stranded on the Greek side of the Promahonas border crossing Wednesday, and about 1,000 trucks and 500 cars on the Bulgarian side. Farmers had been allowing private cars to cross, but the truckers on the Bulgarian side have halted all traffic.