A new constitution was a key demand of the Movement for Democratic Change (MDC) for joining a unity government with President Robert Mugabe, who critics say has rigged polls in the last 10 years to stay in power.
Zimbabweans hope a new charter to replace one inked in 1979 would whittle the president’s powers, strengthen the role of parliament and guarantee civil liberties and political freedoms.
The National Constitutional Assembly (NCA), which has campaigned for a new charter for the past decade, said on Wednesday it opposed parliament driving the process and wanted a "reputable" sitting or retired judge to chair an independent commission, which would include civic groups.
"Our point of departure is that we believe the process is not people-driven, it will be controlled by the political parties and our principles stand against this," NCA Chairman Lovemore Madhuku told reporters.
"We are going to start a process of opposing this process. The NCA will campaign for a ‘No Vote’."
The NCA’s stance sets it at odds with its MDC allies. Together they mobilised Zimbabweans to reject a government-sponsored constitution in a 2000 referendum.
Analysts say opposition from the NCA, which groups political parties, rights groups, churches and activists, would stain the credibility of the current process.
But they also say the NCA, weakened by government crackdowns, may find it impossible to marshal enough support against a new constitution without its MDC allies.
Madhuku also rejected government’s plans to use a draft constitution agreed to by the MDC and Mugabe’s ZANU-PF party in negotiations in September 2007 as a starting point for consultations around the country.
The so-called "Kariba Draft" has not been made public.
Madhuku said the NCA would hold demonstrations and was strengthening its grassroots campaigns to reject the document.
Zimbabwe’s Speaker of Parliament on Sunday announced that the unity government, in which MDC leader Morgan Tsvangirai is prime minister, had assembled a 25-member parliamentary committee to lead the constitutional writing process.
The process would include consultations around the country, and the new constitution would have to be approved by a national referendum to be held by mid-July next year.
But Madhuku said members of the committee were loyalists who would take instructions from the executive and that the NCA was disappointed with its MDC allies in government.
"If you look at the people who are in the 25-member committee, these are loyalists of the various political leaders. The main lead singers are in that committee," he said.
"In 1999 we opposed a process, which in many respects was not as defective as the current one. We made it clear then that no government must superintend a constitutional making process. That remains our position today."