Venezuela's top electoral official Jorge Rodriguez has requested extra security measures following the murder of a local election officer.
President Chavez currently has a majority in the National Assembly
The official, Oswaldo Rodriguez - no relation - was stabbed to death on Thursday night.
The motive is unclear, but Mr Rodriguez said the National Electoral Council faced a campaign of insults and slander ahead of December's congressional poll.
An opposition spokesman accused Mr Rodriguez of exploiting the murder.
Mr Rodriguez said the killing appeared to have been aimed at intimidating the council.
He said his namesake, who headed the council in Amazonas state, and other regional directors had received anonymous death threats by phone.
Oscar Valles of the opposition Sumate group said the murder had been carried out by common criminals.
The opposition argues that the council is biased towards President Hugo Chavez, and that this contributed to his victory in a recall referendum in August last year.
Independent observers found no evidence of fraud in the vote.
Several thousand candidates are taking part in the 4 December elections to the 167-seat National Assembly, where supporters of Mr Chavez currently have a majority.