Passengers travelling between some Swedish cities and to Finland have so far been affected by the strike, which got under way at 7am.
Flights to and from Stockholm and Kalmar, Visby, Åbo and Vasa were called off in the morning. Later on Monday, four evening flights from the Swedish capital to the latter three destinations were also cancelled after afternoon crunch talks between union representatives and the airline failed to arrive at a resolution.
"We hope that the parties that are negotiating do their job and agree on a collective agreement. We are now focusing on taking care of our customers and making bookings for them so that they can arrive at their destinations," said press officer Cathrine Sandgren earlier in the day.
Around 450 travellers are expected to be affected by the strike by the end of the day, according to the airline. However it said the walkout was not expected to have an impact on other routes.
The row between bosses and staff working for Scandinavia's largest airline is focused on the salaries and conditions of around 30 cabin crew who work on SAS flights which are operated by the UK-based budget carrier Flybe.
The staff on the affected routes are employed by a recruitment firm called Global Employer Agency, and the Swedish pilots' union SPF and the Unionen union have been trying to pin down a deal for them since last autumn.
SAS has previously threatened to close down a "large number of regional routes" in the Nordics if unions fail to accept its terms.
The company, which is partially owned by the governments of Sweden, Denmark and Norway, has spent the past few years struggling in the face of growing competition from low cost airlines, including Ryanair and Oslo-based Norwegian, Europe's third-largest budget carrier.
But in September it announced its pre-tax profits were 30 percent higher this summer than in 2014 and said the firm had celebrated its best July for a decade.