Heavy traffic congestion is expected during rush hour on Wednesday as the Korean Confederation of Trade Unions(KCTU) is set to hold a massive rally and march through downtown Seoul.

The event, attended by some 20-thousand members, will kick off near Sejong-daero road at 4 p.m., during which the labor group will declare its forthcoming protest against what they call the government's anti-labor policies and police crackdowns.

The rally will mark the first large-scale gathering since the police vowed to sternly respond to illegal labor activities following an overnight rally by unionized construction workers earlier this month that caused public inconvenience at night.

On Wednesday, construction and metal workers unions will each hold rallies from 2 p.m. and later meet in the Sejong-daero area.

Estimating that some ten-thousand people will gather, the police said on Tuesday that some roads will be cordoned off and alternatives will be prepared for buses, while over 200 officers will be deployed to mitigate the impact on traffic.

The public is advised to take public transport as congestion is expected in downtown areas such as Jongno and Euljiro.