The plan "will be imposed by force and its result will be that constitutional status will be given to a military, socialist, Marxist and communist dictatorship," the head of the Venezuelan Episcopal Conference, Diego Padron, told a news conference.
The church has long had strained relations with President Nicolas Maduro, who is under mounting opposition and international pressure to hold early elections.
The center-right opposition accuses Maduro of maneuvering to cling to power against its demands for a vote on removing him.
It blames him for an economic crisis that has caused shortages of food and medicine. He says the crisis is a US-backed conspiracy.
Catholic leaders tried last year to mediate in negotiations between the government and opposition. The talks collapsed with the sides accusing each other of bad faith.
Pope Francis called this month for "an end to violence and a peaceful and democratic solution to the crisis" in Venezuela.
At least 91 people have died over the past three months in clashes with police during anti-government demonstrations, prosecutors say.
Maduro has meanwhile infuriated his opponents by launching a plan to form an assembly tasked with rewriting the constitution.
Opponents say he will pack this "constituent assembly" with allies in a bid to cling to power.
Voting for members of the assembly is scheduled for July 30.
The opposition MUD coalition plans to hold its own popular vote against the plan on July 16.
Maduro retains the public backing of the military high command -- a key factor in keeping him in power, according to analysts.
But the president last month said he was replacing four senior commanders of the armed forces.
Eyewitness? Submit your stories now via social or:
Email: news@pulselive.co.ke
