Diosdado Cabello (left) and Nicolas Maduro (right) say the constitution allows the inauguration of President Chavez to be postponed
Venezuela's authorities have urged President Chavez's supporters to join a major rally on Thursday, when he is due to be sworn in for a fourth term.
Mr Chavez, in hospital in Cuba after cancer surgery, is unlikely to attend.
But Venezuelan National Assembly Speaker Diosdado Cabello said many heads of state would be in Caracas to show their support.
The Catholic Church says ministers risk violating the constitution and the opposition have called for protests.
The opposition insist new elections should be called within 30 days if Mr Chavez is unable to take the oath on 10 January.
The 58-year-old Venezuelan leader, who has been in power since 1999, has not been seen in public since his latest operation last month, and government officials have acknowledged that he has suffered complications caused by a lung infection.
The president's condition was "stable", Information Minister Ernesto Villegas said in a televised statement late on Monday.
Predicting a major pro-Chavez demonstration, the speaker of the assembly appealed to opposition leaders to act responsibly on Thursday and warned: "We will stop any attempt to destabilise the government".
"There will be a big gathering here in Caracas on 10 January. All of Venezuela is going to come to Caracas and be in front of the Miraflores (Presidential) Palace. The people will be on the streets," Mr Cabello said.
Earlier, the Venezuelan Catholic Church said it would be a morally unacceptable violation of the constitution to allow Mr Chavez to remain in power after missing his inauguration.
The head of the Venezuelan Conference of Bishops, Diego Padron, said Mr Chavez had to attend his inauguration when his term ended on 10 January.
"It is not our job to intervene publically, but in this case the good of the country and the defence of ethics are at stake. To alter the constitution to attain a political objective is morally unacceptable," added Monsignor Padron.
The assembly speaker hit back, insisting that the government "had always respected the constitution and would continue to do so".
"We believe the call made by the Bishops' Conference today is aimed at the sectors of the opposition and the high echelons of the Church who took active part in the 2002 coup attempt (against President Hugo Chavez)," he said.
Diosdado Cabello was re-elected as speaker on Saturday.
If Mr Chavez does not take the oath of office, the Speaker of the National Assembly should act as caretaker president until new elections are held within 30 days, the opposition say.
In the absence of President Chavez, Mr Cabello and Vice-President Nicolas Maduro are in effect running the country.
Attorney-General Cilia Flores said on Sunday that Mr Chavez could be sworn in at a later date.
Mr Chavez is a "re-elected president, not an elected candidate", said Ms Flores, adding that the key date was 7 October when President Chavez was elected for his fourth term.