CARACAS, Venezuela — Venezuela prepared Friday for a possible showdown between opposition protesters and government forces ahead of a vote that critics decry as a final step toward authoritarian rule in the South American nation.

Residents in the sprawling capital poured into supermarkets, already struggling with food shortages, to stockpile what they could amid fears of clashes. Flash points emerged in parts of the city, with clusters of protesters clashing with security forces, who fired tear gas..

“I’m going to stay home all weekend because I feel there will be violence,” said Rosa Aponte, 45, who was shopping in a packed grocery store in wealthier eastern Caracas.

Ahead of Sunday’s vote, the socialist government of President Nicolás Maduro – the anointed successor of leftist firebrand Hugo Chávez, who died in 2013 – issued a ban on public gatherings and protests through Tuesday. The opposition answered with a vow to pour into the streets nationwide.

Opponents are boycotting Sunday’s vote, which would create a super-congress that could prolong Maduro’s rule. The body would possess awesome powers, including the right to change the constitution.