They are furious at the authorities' decision last week to halt their efforts to call a referendum on removing Maduro from power
Venezuela's political rivals are set to engage in a volatile test of strength Wednesday, with the opposition vowing mass street protests as President Nicolas Maduro resists efforts to drive him from power.
The socialist president and the center right-dominated opposition have accused each other of mounting a "coup" in the oil-rich country, stricken by food shortages.
Pope Francis intervened on Monday, granting a private audience to Maduro, who said the sides had agreed to launch a "national dialogue" to settle the crisis.
Leaders in the broad opposition coalition MUD denied they had reached an agreement with the government on the terms of any possible talks.
They are furious at the authorities' decision last week to halt their efforts to call a referendum on removing Maduro from power.
They have called for massive nationwide protests on Wednesday -- the first such rallies since hundreds of thousands of MUD supporters filled the streets of Caracas on September 1.
Maduro for his part called a meeting on Wednesday of his so-called National Defense Council, which includes the heads of the various branches of government.
He flexed his muscle on Tuesday with a rally of thousands of supporters.
Analysts have warned of a risk of violent unrest in Venezuela. Clashes at anti-government protests in 2014 left 43 people dead.
On Monday a students' group said 27 people were injured in clashes with police at a protest in the western city of San Cristobal.
Hit by the fall of global oil prices, Venezuela's economy has crashed, sparking protests and looting driven by shortages of food, medicine and basic goods.
Maduro calls the economic crisis a capitalist conspiracy. The opposition blames his economic management.
A recent poll found that more than 75 percent of Venezuelans disapprove of Maduro. But he has vowed to resist efforts to sack him before his term ends in 2019.
Maduro accused the opposition-majority legislature on Tuesday of staging a "parliamentary coup" after lawmakers voted to open a political trial against him over the crisis.
Maduro fired back by summoning the defense council. "We will not permit a parliamentary coup of any kind," he told cheering supporters.
It was unclear what impact Tuesday's legislative vote will have.
The Supreme Court has overruled the National Assembly's decisions since the opposition majority took over in January.
The opposition claims Maduro controls the court and the electoral authorities and has used them to block the referendum.
Maduro accused the "useless" legislature of trying to "harm Venezuela," and urged his opponents to agree to the talks.
That offer initially appeared to have sown divisions in the Democratic Unity Roundtable (MUD), a shaky coalition united mainly by shared hatred of Maduro.
Some of its leaders said they had only learned on TV about the proposal to hold negotiations on the Caribbean island of Margarita from next Sunday.
They insisted any talks be held in the capital Caracas for greater transparency.
The MUD said it would only agree to talks if the government respected the constitutional right to a referendum and freed its imprisoned activists and leaders, among other demands.
Leading opposition figure Henrique Capriles accused Maduro of using the pope's goodwill for his own ends.
"They are devils," he said of Maduro and his allies.
"They believe in nothing, they have no principles. They say they're Christians when it's convenient."
Political analysts were skeptical about the prospects for talks to resolve the crisis.
"Even if Pope Francis comes here dressed up as Superman, dialogue won't resolve" Venezuela's problems, said political scientist Nicmer Evans.