With Venezuela's economy in recession, oil revenues plunging and consumers facing chronic shortages of basic goods, Maduro's approval rating has sunk to 28 per cent, a crisis for the movement founded by his late mentor, leftist firebrand Hugo Chavez.
Maduro's United Socialist Party of Venezuela (PSUV) and its allies risk of losing the National Assembly for the first time since Chavez came to power in 1999, according to an April survey, which found the PSUV and its allies had 25 per cent support against 45.8 per cent for the opposition.
The head of the National Electoral Council, Tibisay Lucena, denied the charge, accusing opposition groups of seeking to "discredit" the organization.
"The National Electoral Council does not work under pressure," she said.
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Lucena announced the official campaign period would run from November 13 to December 3, with candidate registration from August 3 to 7.
Jailed opposition leader Leopoldo Lopez has been on hunger strike for 30 days to insist the government set a date for the election and to guarantee that it will be overseen by international observers.
Lopez and Ceballos are both charged with inciting violence during protests that shook the country last year, when Venezuelans poured into the streets.
A police crackdown and violence between pro- and anti-government demonstrators left 43 people dead and hundreds wounded.
The protest movement faded in July after months of unrest and the detention of top opposition leaders.