A fourth Venezuelan opposition party has withdrawn from this Sunday's congressional election amid a dispute over electronic voting machines.
Preparations for Sunday's election are under way
Primero Justicia's decision means more than half the opposition groupings have now pulled out.
Opposition parties are worried the election board could rig the vote.
Electoral officials deny such accusations and say voting for the expanded 167-seat Congress will go ahead as planned.
The government of President Hugo Chavez has vowed to increase its majority to two-thirds, which would allow it to pass constitutional reforms that opposition leaders strongly oppose.
Venezuelans will vote for an expanded 167-seat Congress
Two seats were added since the last election
Supporters of President Hugo Chavez hold 52% of the seats and hope to increase its majority to two-thirds
120,000 soldiers will watch voting stations
The poll will be overseen by the Organization of American States and the European Union
Three other opposition parties pulled out of the poll earlier this week, accusing the electoral body of favouring pro-government candidates.
They are the main opposition party Democratic Action, Project Venezuela and the Social Christian party.
President Chavez hit back, claiming the opposition was trying to derail the election and accusing them of plotting with the US to destabilise the country.
President Chavez's backers have called a rally on Thursday in support of the congressional election.
Washington has said it is increasingly concerned about the state of Venezuela's democracy, but denies helping the opposition parties.
Democratic Action leader Henry Ramos has called for a suspension of the election until equal conditions existed for parties.
He told reporters earlier this week that there were 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.
Representatives of the electoral council have repeatedly denied accusations of a pro-government bias.
Mr Chavez's backers have called a rally in support of the poll
The authorities had removed fingerprint machines at polling stations after opposition leaders said the identification system threatened voter confidentiality.
But the concession failed to assuage some opposition parties.
The BBC correspondent in Caracas, Greg Morsbach, says that despite the boycott, a number of 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.
The poll on Sunday will be overseen by observers from the Organization of American States and the European Union.