Seoul’s subway workers launched a work-to-rule protest Wednesday, delaying trains during morning rush hour.

As the main union at Seoul Metro, accounting for 60 percent of all unionized workers at the company that operates lines 1 through 8, began the collective action, some sections reported delays of up to 20 minutes.

Under the work-to-rule protest, the union is refusing work outside of what is stipulated in the regulations.

The workers are demanding a wage hike of at least five percent next year and withdrawal of the management’s plan to introduce a single-attendant system amid restructuring efforts.

If the demands are not met, the union intends to stage a general strike on December 6 for the third consecutive year.