The Seoul subway is in talks with its three affiliated unions a day ahead of their planned strike for a wage hike and increased workforce.

According to sources close to the two sides, collective bargaining will likely continue until late Thursday or early Friday. The three unions have declared their intent to strike on Friday morning if they fail to reach a deal.

The unions are urging Seoul Metro, the operator of Subway Lines 1 through 8, to increase wages by three percent this year, as set by the government for the public sector, and to fold bonuses into regular salaries.

The workers are also calling for new hires, but Seoul Metro says those would first require the city's approval.

If negotiations fall through and the unions go on strike, commuters in the capital region will likely suffer major traffic disruptions.

The city government plans to dispatch an essential workforce and substitutes to ensure regular operation during the morning rush hour and to maintain 88 percent operation during the evening rush hour, while extending intracity bus operations by one hour.