Finnair has announced it will cancel approximately 140 flights on Friday, affecting around 12,000 customers travelling on May 2.
The four-hour industrial action is due to take place on Friday, according to the Finnish Aviation Union (IAU), which indicated the work stoppage will take place in "different shifts" rather than at a specific time.
Finnair's chief operating officer, Jaakko Schildt, said: "We are sorry for the situation and will do everything we can to ensure that every customer receives a suitable new routing as soon as possible."
The carrier warned that "due to the high number of cancellations, re-routing all customers may take time".
The industrial action will take place in different shifts
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The strike is expected to impact multiple functions at Helsinki Airport, including flight operations and ground services.
Some short-haul flights on Friday may operate without baggage and meals loaded onto the aircraft.
According to the airline, long-haul flights will not be affected by catering limitations.
Helsinki Airport has warned travellers to expect flight delays and "occasional queues" on the day of the industrial action.
The work stoppage will significantly disrupt normal operations throughout the airport's busiest terminals.
Customers affected by the cancellations can either accept a new routing or cancel their reservation and apply for a refund.
Finnair has stated it is working to accommodate all affected passengers as quickly as possible.
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Helsinki Airport has warned travellers to expect flight delays
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The disruption is not limited to Friday's operations, as the IAU has announced similar industrial action for Monday May 5.
Finnair said it is "still assessing the exact effects" of Monday's planned strike on traffic.
The airline warned that the second round of industrial action is likely to cause additional disruption to services.
Helsinki Airport has also cautioned travellers about potential flight delays and queues on both strike days.
