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.