Several hundred Sweden-based pilots walked off work Friday, disrupting about 40 flights operated by Scandinavian airline SAS, the carrier said.
The strike among 350 pilots began shortly after 6 pm (1600 GMT) after mediated talks failed to bridge differences between the Swedish pilots' union and employers.
The union on Thursday also rejected a bid, saying they wanted wage increases of 3.5 per cent and revisions in the collective bargaining agreement.
The Swedish Aviation Industry Group, which organizes employers, offered 2.2 per cent.
The conflict affected domestic Swedish and European routes from its Stockholm base, but not long-haul flights.
SAS estimated about 4,000 passengers were affected on Friday, spokeswoman Karin Nyman told Swedish Radio.
Passengers were advised to consult the carrier's website or the company they booked tickets.
Earlier Friday, the carrier reported a drop in second quarter profits, citing tougher competition, higher costs for technical maintenance and currency effects.
The net profit of 171 million kronor (21 million dollars), compared with 279 million kronor in the corresponding period a year ago.
Revenue in the February to April period was 8.92 billion kronor, down from 9.4 billion kronor a year ago.
In neighbouring Norway, SAS averted a pilot strike Thursday after mediated talks went into overtime.
The airline - whose main owners are the governments of Denmark, Norway and Sweden - is facing stiff competition from low-cost carriers such as Norwegian Air Shuttle.