Updated

Labor leader Froilan Barrios on Thursday announced his presidential candidacy in hopes of challenging incumbent Hugo Chavez in December elections, while promising to defend the interests of Venezuela's workers.

Barrios, a representative of the Venezuelan Workers Confederation, said he would participate in a primary election to choose a single opposition candidate ahead of the Dec. 3 vote.

"If we don't live in democracy, we won't be able to make minimal labor demands," said Barrios, accusing Chavez of becoming increasingly authoritarian and trying to weaken labor organizations.

Sumate, a pro-democracy group aligned with the opposition, has invited all of Venezuela's opposition parties to participate in the primary and set June 16 as a tentative date for the vote. Sumate plans to organize the primary without help from the National Elections Council, which some Chavez foes view as too government-friendly.

Supporters of the primary say Venezuela's diverse opposition movement must field a single candidate to defeat the leftist president.

Six challengers have announced plans to run against Chavez, although not all of them have agreed to participate in primaries to choose a single opposition candidate.

The five other opposition candidates are Luis Vicente Brito, a business leader; Teodoro Petkoff, a newspaper editor; William Ojeda, a journalist and former Chavez ally; Julio Borges, a conservative attorney; and Roberto Smith, an ex-infrastructure minister.

Chavez was elected in 1998 and re-elected in 2000 on promises to redistribute Venezuela's immense oil wealth and fight rampant corruption in public administration.