The opposition on Friday filed a case with prosecutors alleging that the government, judges and electoral officials were conspiring "to violently change the constitution," lawmaker Tomas Guanipa said.
The move came after Attorney General Luisa Ortega on Thursday mounted a separate challenge in the Supreme Court against President Nicolas Maduro's efforts to rewrite the constitution, in a sign of division within the government camp.
Various opponents of Maduro also went to the court on Friday to try to add their names to the list of plaintiffs in that lawsuit, but found the tribunal closed and blocked by riot police vans.
Opposition lawmaker Delsa Solorzano told reporters that armed government supporters beat her group as it was leaving.
Clashes at daily protests by demonstrators calling for Maduro to quit over an economic crisis have left 66 people dead since April 1, prosecutors say.
Maduro has launched moves to reform the constitution in response to the protests, but his opponents say that is a ploy to cling to power.
Maduro says the crisis is a US-backed conspiracy.
Ortega is the highest-profile official to defy him in the crisis.
Maduro retains the public backing of the military. However, its commander Vladimir Padrino Lopez sounded a moderate note this week when he warned security forces against attacking protesters.
Analysts said Ortega's suit could build bridges between the opposition and disgruntled officials and widen divisions in Maduro's camp, making it harder for him to stay in power.
"The attorney general has proposed something that they all agree on, the radical and moderate opposition and the radical and moderate critics" of Maduro within his own camp, political analyst Felix Seijas said.
"There is near-unanimous support for it. A bridge has been raised to join the two sides together."
In the latest rallies on Friday, some 2,000 demonstrators led by student groups marched in Caracas to the National Telecommunications Commission to protest what they call state censorship of the media and repression against journalists.
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