Unionists of HD Hyundai's three shipyard units hold a rally to demand the start of this year's wage talks in front of the group's office in Seoul, July 18. Yonhap

Unionized workers at HD Hyundai's three shipyard units kicked off a joint strike vote Monday amid little progress in their collective negotiations.

Unionists at the three shipbuilders ― Hyundai Heavy Industries, Hyundai Mipo Dockyard and Hyundai Samho Heavy Industries ― are slated to cast votes till Wednesday, according to union officials.

It marks the first time that the labor unions of the shipbuilders have held a joint strike vote.

The outcome of the vote is due late Wednesday, with unionized workers widely expected to vote for a strike.

The trade unions said they are planning to discuss whether to go on a strike if unionists deliver a yes vote.

Even though collective negotiations have been under way at each shipyard, little progress has been made so far.

Unionized workers are asking for contracts that include a 142,300 won ($99) hike in base pay and the abolition of a wage peak system.

In July, the three unions came up with a joint collective bargaining demand, but the companies say joint collective negotiations are not desirable because they are separate entities and have different situations.

HD Hyundai, formerly Hyundai Heavy Industries Holdings, is a shipbuilding, oil refining and machinery conglomerate in Korea. The three shipyards are under the wing of Korea Shipbuilding Offshore Engineering, the group's shipbuilding subholding company.

Hyundai Heavy Industries and Hyundai Mipo Dockyard are based in the southeastern industrial port of Ulsan, while Hyundai Samho Heavy Industries is headquartered in Yeongam on the southwest coast. (Yonhap)