U.N. sponsored talks on reunifying Cyprus have suffered a blow after Turkish Cypriot leader Mustafa Akinci backed out of Thursday’s meeting.

The Turkish Cypriots are angered over a bill passed by the Greek Cypriot parliament ordering schools to celebrate a 1950 referendum calling Cyprus part of Greece. The vote had no legal standing at that time.

Akinci says the bill must be rescinded if the talks are to continue.

Greek Cypriot President Nicos Anastasiades says he regrets Thursday’s session has been canceled and said on Twitter he is ready to resume talks at any time.

He says it was a mistake for lawmakers to pass the bill at such a sensitive time, but also said it is a shame the peace talks have been put in jeopardy over what he calls a minor issue.

Cyprus has been split between a Greek Cypriot south and Turkish Cypriot north since 1974, when Turkish troops invaded the island after a military coup intended to unify the island with Greece.

Only Turkey recognizes a separate Turkish Cypriot governor. The international community recognizes the Republic of Cyprus and the entire island, while divided, enjoys European Union membership. 

The most recent talks to reunify the island have been under way for more than two years. The issue of whether Turkish forces can remain on Cyprus after the island is whole again has been the major hold-up of a final settlement.