Scandinavian airline SAS said 230 flights were cancelled on Monday, affecting 27,000 passengers, after new efforts failed to end a strike by Sweden-based pilots over wages.
Domestic Swedish and European flights including to other Nordic capitals as well as Frankfurt, Paris and London were disrupted.
Over the weekend an estimated 50,000 passengers, including several thousand charter tourists, had already been affected when 380 flights were cancelled due to the labour action.
Mediated talks, which began Sunday, broke off at 01:30 am (2330 GMT) without agreement.
It was not immediately clear when flights would return to normal.
"We have done all that's in our power to avoid a continued strike, but we have unfortunately still been unable to come to an agreement," SAS spokeswoman Karin Nyman said in a statement.
The industrial action began Friday, when talks between the Swedish pilots' union and SAS broke down, leading the union to call its 400 Sweden-based pilots out on strike.
The union said they wanted wage increases of 3.5 per cent and revisions in the collective bargaining agreement. SAS pilots said they want compensation for wage cuts and other concessions they made 2012 when the company was in dire straits.
The Swedish Aviation Industry Group, which organizes employers, offered 2.2 per cent, saying that was in line with other groups.
Danish and Norwegian pilots were flying as normal, the company said.
Passengers were advised to consult the carrier's website or the company with which they booked tickets.
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.