Union members at Hyundai Heavy Industries (HHI) are carrying out strikes this week in a pay dispute.
Workers walked out for four hours on Wednesday and said they would do the same again on Thursday, the Yonhap news agency reported.
The move came ahead of a decision due on Thursday by the labour relations commission on whether to accept a plan by the company to cut wages for offshore division workers by 40%.
The union has 12,000 members eligible to take part in industrial action.
The offshore division won its first order since 2014 this month, signing a $454m contract with LLOG of the US.
