Dozens of people sat down on the main highway into Caracas in the early morning and similar rallies were called around the country.
Dozens of people sat down on the main highway into Caracas in the early morning and similar rallies were called around the country. Rallies over recent weeks have drawn thousands.
Clashes have left 38 people dead in protests against moves to strengthen President Nicolas Maduro's hold on power and his refusal to hold early elections.
The center-right opposition blames Maduro for an economic crisis that has caused severe shortages of food and medicine.
A senior opposition lawmaker, Freddy Guevara, told reporters Monday's rally would go on for 12 hours until 2300 GMT.
He said 50 other similar "sit-ins" were planned on roads across the country with the aim of generating a state of "ungovernability" to pressure Maduro.
"This is a day of resistance, of endurance, of showing that we are organized and firm," Guevara said at the rally.
He repeated the opposition's claim that Maduro was installing a "dictatorship."
Maduro has vowed general elections will take place as scheduled in late 2018 but not before.
He has accused the opposition of mounting an "armed insurgency" with US backing to remove him from power.
He has set no date for postponed regional polls and for mayoral elections that are due this year.
The opposition has called on the armed forces to stop backing Maduro but so far he still has the public backing of the high command.