Venezuelan President Hugo Chavez has urged voters to approve constitutional changes in a referendum on Sunday.
Addressing tens of thousands of supporters at a rally in Caracas, he also threatened to stop oil supplies to the US if it tried to disrupt the vote.
The reforms include allowing abolishing presidential term limits and ending the autonomy of the Central Bank.
Mr Chavez said the proposed changes would return power to the people, but critics accuse him of a power grab.
Mr Chavez said that his opponents could try to sabotage the vote, with backing from Washington, through violent protests.
He said: "If this [referendum] is used as a pretext to start violence in Venezuela, Energy Minister Rafael Ramirez on Monday will order that oil exports to North America be stopped."
He added that troops had been sent to "protect" the country's oil fields.
Indefinite re-election of president, term increased from 6 to 7 years
Central Bank's autonomy ended
Structure of country's administrative districts reorganised
Maximum working day cut from 8 hours to 6
Voting age lowered from 18 to 16
Social security benefits extended to workers in informal sector
Mr Chavez has accused Washington of conspiring to topple his government and possibly backing plots to assassinate him. US officials have called the accusations ridiculous.
On Sunday, voters will be asked whether they agree with a package of constitutional reforms.
Mr Chavez proposed 33 changes, and the National Assembly, which is composed of his supporters, put forward a further 36 amendments.
His opponents have called for close monitoring of the ballot. Opinion polls have suggested that the result could be close, although surveys in the past have tended to underestimate the level of support Mr Chavez enjoys.
The BBC's Americas editor, Emilio San Pedro, says the elections are expected to be as free and fair as all previous ones since Mr Chavez came to power in 1998.
One proposal is to allow the president to stand for re-election an indefinite number of times.
Speaking on Friday, Mr Chavez said: "If God gives me life and help, I will be at the head of the government until 2050." He would be 95 years old.
Venezuela's national assembly voted through the reform package
Under the current constitution, Mr Chavez would have to stand down when his term expires at the end of 2012.
Other changes up for approval include giving the president control over the central bank, the creation of new provinces governed by centrally-appointed officials, and a reduction in the voting age from 18 to 16.
There are also proposals to expand presidential powers during natural disasters or political "emergencies".
On the social front, changes include establishing a maximum six-hour working day and 36-hour working week, and widening social security benefit to workers in the informal economy.
A number of defections from the president's camp have encouraged opponents, but Mr Chavez has dismissed these one-time allies as traitors.