Hyundai Motor sold fewer than 50,000 cars here in August, the first time in 11 months that the figure dropped below the benchmark. The total was 48,143.
The carmaker's exports also fell 25 percent on-year to 64,405 units.
Hyundai attributed the dip to fewer working days due to summer holiday as well as partial industrial action.
Affiliate Kia also saw domestic sales down 9.8 percent on-year.
Meanwhile, Renault Samsung sold a mere 4,741 cars in August, a seven-percent decrease from a year earlier. Besides fewer business days and partial labor strikes, it also cited a drop in supply of the QM3 compact SUV, which is imported from Spain.
Wage negotiations continue.