One of South Korea's umbrella labor unions has hinted at the possibility of staging a massive strike in protest of recent arrests of three of its senior members on charges related to their illegal acts while rallying in front the National Assembly.

Calling for the release of its members on Friday, the Korean Confederation of Trade Unions(KCTU) said it has no other choice but to turn its planned strike in July into one condemning the Moon Jae-in administration.

The KCTU had previously announced the strike, calling for permanent working status for contract workers in the public sector.

On Thursday, the Seoul Southern District Court issued arrest warrants for the three members for their alleged plan to obstruct justice and other illegal acts during rallies in late March and early April to protest labor reforms.