Venezuela's opposition is refusing to take part in an audit of the vote on President Hugo Chavez's rule, which electoral authorities say he won.
The Venezuelan opposition is crying foul
Opposition leaders said the review would not properly investigate their allegations of massive fraud.
They are calling for checks to include touch-screen voting machines, saying many were rigged - allegations rejected by electoral officials.
International election monitors have endorsed the result.
The audit is being carried out by the official electoral authority - the Venezuelan National Electoral Council - and international observers from the Carter Center and the Organization of American States (OAS).
They were due to visit 150 randomly chosen polling sites, checking the results produced by voting machines against paper records, in the presence of government and opposition representatives.
But a senior member of the opposition, Nelson Rampersad, demanded a far wider probe - to include the machines themselves as well as the software.
He told journalists that many stopped recording votes against Mr Chavez once a ceiling had been reached.
Mr Chavez, whose populist policies have split Venezuelan opinion, officially won Sunday's poll with 59% of the vote.
'No reason for doubt'
Announcing the audit on Tuesday, former US President Jimmy Carter said he and the OAS had suggested the move to allay fears over the validity of the outcome.
He stressed that he himself had "no reason to doubt the integrity of the electoral process or the accuracy of the referendum itself".
Paper and electronic returns will be compared at random
Mr Chavez has urged the opposition to have the "grace" to accept the result and called for national reconciliation.
And some opposition figures have begun saying the referendum result should be accepted.
"We have to bite the dust of defeat," Manuel Rosales, governor of Zulia state, was quoted as saying by the Associated Press news agency.
The head of the country's biggest business association, Fedecameras, has also called for reconciliation between Chavez supporters and opponents.
"These two Venezuelas must reconcile. Venezuela cannot continue in conflict," said Albis Munoz.
The opposition has fought a tireless campaign to see Mr Chavez ousted. The president survived a short-lived coup in April 2002 and a two-month strike that badly damaged the economy later that year.
The referendum was activated after the opposition collected signatures from 20% of the population - a recall mechanism inserted into the Venezuelan constitution by Mr Chavez in 1999.