Pilots have meet the management at Korean Air for talks to try to resolve their strike, as the government threatens to intervene.
Dozens of cargo and passenger flights have been hit
The pilots began their walkout on Thursday, demanding higher pay.
Their union and the firm, South Korea's largest airline, met briefly on Friday but no breakthroughs were reported.
With about 60% of the airline's flights cancelled, the government has said it is prepared to use emergency powers to force the pilots back to work.
Finance Minister Han Duck-soo said: "It is regretful that the Korean Air pilots' strike is causing damage to the economy and inconvenience for people."
"The government should prepare all possible measures, including the power to stop the strike and bring in emergency mediation, because the intangible losses are increasing," he told an economic co-ordination meeting.
The Korean authorities broke up a strike by pilots at Asiana Airlines this summer after it entered its 25th day.
Emergency powers enable the government to intervene in strikes affecting industries which are critical to the national economy.
Korean Air carries about half of the country's air cargo, including major exports such as semiconductors and mobile phones.
A ruling party official said December was the busiest month for exports.
About 500 pilots held a rally near Seoul on Thursday and more are expected to join the strike in coming days.
Korean Air says the strike is costing it about 25 billion won ($24m) a day.
The carrier expects increased disruption on Friday
Unions representing about two-thirds of the airline's pilots are pushing for an 8% rise in annual pay.
The carrier has rejected this demand, offering a 3% rise instead.
It said the workers' demands were unrealistic, given rising fuel costs and fierce competition in the airline sector.
Only this summer strike action was narrowly avoided after Korean Air reached agreement with unions on minimum rest times for pilots after international flights.
Before the Asiana strike, the emergency powers had only been used twice - in 1969 and 1993.
They enable the government to order a return to work and negotiations. If no settlement is reached the government can dictate one.
"We will first try to lead them to reach an agreement voluntarily and keep a close eye on further developments," said labour ministry spokesman Jung Hyun-ok.