President Moon Jae-in on Tuesday reiterated his policy drive to enhance labor rights as a concern involving "our own values and dignity."

In a statement marking Labor Day, Moon also defended the upcoming reduction in working hours to 52 hours a week from the current 68 hours, while voicing dismay over a failure to achieve an early constitutional revision aimed at strengthening labor rights.

"On the occasion of Labor Day, I think of a world in which labor is not given short shrift or mortified by institutions or those in power. ... The government will make continued efforts for a society that respects labor," Moon said.

"There is no greater growth than the value and dignity of labor. ... All growth should be growth for workers," he added.

Moon's labor policy has been a focus of conservatives' political attacks. His detractors have condemned it as part of his "leftist" thinking or even an attempt to instill socialist views in South Korea's democracy.

Moon, however, doubled down on his initiative with an increase in the legal minimum wage, the planned cut in working hours and policy efforts to turn contract-based irregular workers into regular ones, among other things.

"Labor is lofty ... The oil stains stuck in our fathers' nails have propped up our lives, and the soil in our mothers' nails have led grain to grow like the hope (we have)," Moon stressed.

He expressed regret about the failure to hold a national referendum on a constitutional revision at the same time as the June local elections and vowed to improve labor rights through policy efforts.

Through the revision, Moon has sought to improve public officials' labor rights, the workers' right to collective action and ensure the same wage for the same work, to name a few proposals his government made for the revision.

Amid partisan squabbles over a range of politically charged issues, the parliament has failed to pass a revision to the national referendum act, seen as a pre-step to set up a plebiscite on the revision. Thus, Moon's plan to hold the public vote on the referendum in June failed.

Meanwhile, the Korean Confederation of Trade Unions, an umbrella labor group, staged a massive rally in downtown Seoul, calling for greater efforts to enhance workers' rights.

Under the rallying cry, "Create a new labor (environment) in Korean society," the KCTU highlighted a series of union demands, such as an end to unfair layoffs, the same wage for the same work, and the elimination of workplace sexual abuses and discrimination against migrant workers.

"We make a declaration for Korean society where the right to work is guaranteed for all," Kim Myoung-hwan, the KCTU chief, told a gathering of some 10,000 people at Seoul Plaza.

The Korean Government Employees' Union, the Korean Teachers and Educational Workers' Union and other groups held their own rallies. (Yonhap)