The investigation came as the Korea Wood Panel Association, a union of South Korean plywood producers, filed a petition claiming that Vietnamese products have led to a decrease in their earnings.
Plywood is used to produce construction materials and furniture.
South Korea's market for plywood was estimated at 800 billion won ($677 million) in 2018, with Vietnamese products accounting for 40 percent. Local firms took up around 10 percent of the market, the commission said.
The preliminary result of the probe will come out before April 2020.
Currently, South Korea imposes anti-dumping tariffs ranging from 3.96 percent to 38.1 percent on plywood imported from Malaysia and China.
The association claimed that South Korea should slap an anti-dumping tariff of 93.5 percent on Vietnamese plywood. (Yonhap)