Shipyard workers at the main Ulsan yard of Hyundai Heavy Industries (HHI) have staged a protest by downing tools and occupying a crane.

The industrial action at the world’s largest shipbuilding facility took place following a dispute during ongoing wage negotiations.

HHI is one of the shipbuilding companies operating under Korea Shipbuilding & Offshore Engineering (KSOE), which is the shipbuilding arm of Hyundai Heavy Industries Holdings.

According to local reports the demonstration took place on Tuesday with the occupation of a 40-metre-high crane and hundreds of workers gathering around it in protest.

A smaller protest continued into the following day. Sources close to the yard confirmed the industrial action but described it as “small”. HHI's Ulsan facility employs 12,500 people.

The company has had relatively good industrial relations over recent years. Occupying cranes is a traditional form of industrial action at South Korean shipyards, but the last time it happened at Ulsan was in 2004.

The wage row comes at a time when management will be keen to keep a lid on costs at the yard after being hit by significant increases in the price of steel plate.

There is also uncertainty over the HHI's future expansion. A proposed acquisition of a majority stake in compatriot Daewoo Shipbuilding & Marine Engineering has been hit by continued delays due a failure to secure regulatory approval from foreign governments.

The deal has yet to win competition approval from the European Union and Japan. The EU has requested further information from HHI over the acquisition. In its latest filing, HHI said it is now hoping to conclude the deal by 30 September.