Venezuelan President Hugo Chavez has accused the opposition of trying to derail Sunday's congressional election.
Mr Chavez is a vocal critic of the US
Three parties pulled out of the poll on Tuesday, accusing the electoral body of favouring pro-government candidates.
Mr Chavez said the opposition was plotting with the US to destabilise the country, but it denied the allegation.
Venezuelans will vote for an expanded 167-seat congress, where supporters of the president have a majority.
The government has vowed to increase its majority to two-thirds, which would allow it to pass constitutional reforms that opposition leaders strongly oppose.
Mr Chavez again accused political rivals of receiving US financial backing, a claim Washington and opposition leaders have denied.
"They should accept the truth that they have no public. It is an attempt at political sabotage," Mr Chavez said.
But Henry Ramos, chief of the main opposition party Democratic Action, said his only concern was that fairness was not ensured in the congressional election.
"We do not sit on the US ambassador's lap," he said.
On Tuesday, Mr Ramos said Democratic Action was demanding a suspension of the elections until equal conditions existed for parties.
He told a news conference that his party had detected software "irregularities" in the electronic voting machines.
Mr Ramos also cited lack of access to official voting lists and "deep" mistrust of the National Election Council (CNE), most of whose members are in the ruling party.
The authorities had removed fingerprint machines at polling stations earlier this week, after opposition leaders said the identification system threatened voter confidentiality.
But the concession failed to assuage some opposition parties.
Project Venezuela and the Social Christian party said they too were withdrawing and called for a suspension.
The BBC correspondent in Caracas, Greg Morsbach, says that despite the boycott, four other opposition parties are still committed to taking part.
He adds that divisions within the opposition are likely to contribute to a landslide government victory, which would give President Chavez complete control of congress.
Members of the electoral council have repeatedly denied accusations of a pro-government bias.
The poll on Sunday will be overseen by observers from the Organization of American States and the European Union.