Montenegrin President Filip Vujanovic sent an open letter to Serbian President Boris Tadic expressing dissatisfaction with Kostunica's behaviour.
Vujanovic said Kostunica was aware that Montenegro had a law on referendum from 2001 which stated that only Montenegrins with residence in Montenegro can vote in the referendum.
He recalled that by signing the Belgrade Agreement and amendments to the Constitutional Charter Belgrade had given up the right to define conditions for the referendum, which he said was the sovereign right of Montenegro and its citizens.
He particularly objected to the fact that Serbian citizens were being listed according to their ethnicity.
Kostunica's act was also condemned by Montenegrin Parliament Speaker Ranko Krivokapic, the Democratic Party of Socialists, and the Social Democratic Party.