Commonwealth secretary-general Patricia Scotland, KC, says she is concerned by rising tensions between Guyana and Venezuela.
Venezuela's planned actions, she said, "go against the spirit of peaceful dispute resolution.
Before the International Court of Justice (ICJ), the two countries are at odds over which can rightfully claim the Essequibo region. It's currently controlled by Guyana.
On December 3, the Venezuelan government will host a referendum on the issue, in which 20.6 million people are eligible to vote.
In a press release on Wednesday, Scotland said, “The Commonwealth stands with the government and people of Guyana and with our partners in Caricom in expressing our concern over the questions in the planned referendum."
She said the Commonwealth "continues to stand for the rule of law and reaffirms its firm and steadfast support for the maintenance and preservation of the sovereign and territorial integrity of Guyana, and the unobstructed exercise of its rights to develop the entirety of its territory for the benefit of its people."
The questions set to be asked at the referendum, she said, undermine Guyana's territorial integrity and sovereignty.
"Their intent is contrary to international law.
"Question five proposes the creation of Venezuelan state of Guyana Essequibo and an accelerated plan for giving Venezuelan citizenship and identity cards to the Guyanese population. International law prohibits the seizure and annexation by one country of the territory of another."
Scotland said the language used in the questions contributes to heightened tension and is a threat to peace and stability in the Caribbean.
"...The Commonwealth supports the use of the ICJ to adjudicate on the matter.
The referendum, to be held one month before presidential elections in Venezuela, goes against the spirit of peaceful dispute resolution."