The unofficial referendum will take place two weeks before President Nicolas Maduro is asking Venezuelans to go to the polls to choose delegates for a special assembly to rewrite the constitution.
Venezuela's opposition called Monday for a popular vote on July 16 over the government's constitutional reforms which it brands a ploy to cling to power in a deadly political crisis.
The opposition, starting a fourth month of street protests against the socialist government it decries as a dictatorship, will organise the symbolic vote for July 16 as part of its strategy to delegitimise the unpopular President Maduro.
"Let the people decide!" said Julio Borges, the president of the opposition-led National Assembly, confirming what two senior opposition sources said earlier on Monday.
Venezuelans will also be asked their view on the military's responsibility for "recovering constitutional order" and the formation of a new "national unity" government, the Democratic Unity coalition announced.
The opposition's planned vote, likely to be dismissed by the government, would be two weeks ahead of a planned July 30 vote proposed by Maduro for a Constituent Assembly with powers to reform the constitution and supersede other institutions.
"The government is trying to formalise dictatorship," said opposition leader Henrique Capriles, warning the South American OPEC nation was approaching "zero hour."
According to a recent survey by pollster Datanalisis, 85 percent of Venezuelans are opposed to rewriting the constitution, which was reformed by the late leader Hugo Chavez in 1999.
Maduro, 54, Chavez's unpopular successor, says the assembly is the only way to bring peace to Venezuela after the deaths of at least 84 people in and around anti-government unrest since the start of April.
"The people have a right to vote and the people will vote on July 30, rain or shine," Maduro said to cheers during a speech at an open-air event on Monday with candidates to the new assembly.
Opponents say Maduro's plan is a ruse to consolidate the ruling Socialist Party's grip on power and avoid a conventional free election that opinion polls show he would lose. They also accuse the government of threatening people with layoffs or loss of state-provided homes if they do not vote.