The Korea Confederation of Trade Unions, the more militant of the nation's two umbrella labor organizations, on Monday declared its political endorsement for two progressive candidates in the country's presidential election.

In a press conference held in Seoul, the KCTU said it supports Sim Sang-jeung of the Justice Party and Kim Sun-dong of the People's Union Party. The official declaration of support came on the sidelines of a ceremony marking Labor Day.

Sim and Kim are considered the most progressive candidates in the presidential election to be held next Tuesday.

Kim, for instance, is a former lawmaker of the former Unified Progressive Party, which was dissolved late 2014 by a Constitutional Court ruling that decided the party and its activities were pro-North Korea. His People's Union Party is also considered a de facto successor of the now defunct progressive party.

The KCTU's official declaration of support for the two progressive candidates came one day after the Federation of Korean Trade Unions, the larger of the two umbrella labor organizations here, announced its support for presidential front-runner Moon Jae-in of the liberal Democratic Party.

In the latest poll released Sunday, Moon enjoyed an approval rating of 42.6 percent, maintaining a wide distance from runner-up Ahn Cheol-soo of the People's Party with 20.9 percent.

Sim placed fourth with 7.6 percent while Kim and eight other minor presidential hopefuls were not even included in the survey.

"Votes secured by Sim Sang-jeung and Kim Sun-dong can never be considered dead votes. Each vote they win will become a source of power in our fight in the future," the KCTU said. (Yonhap)