The airline on Thursday morning said it had cancelled all internal flights in Norway, and most in Sweden and Denmark, as the unions confirmed that there had been contact with the company's management for the first time since the strike began on Saturday.
"There has been activity and dialogue during the night, but unfortunately I cannot say more than that," Hans-Erik Skjæggerud from Norway's Parat Union told NRK on Thursday morning.
"There is no solution so far," he stressed. "We will continue the dialogue with the company throughout today."
However, Norwegian spokesperson Anne-Sissel Skånvik told Reuters newswire that that the two sides remained "far apart".
At 8am, just 19 Norwegian flights were expected to depart from Oslo's Gardermoen Airport on time, with more than 70 cancelled and seven delayed.
In a statement on its website the company said it hoped to be able to run its ordinary European traffic as normal.
Lithuania's Small Planet Airlines, described on its website as “Europe’s fastest growing charter airline”, started serving holiday makers from the Baltic States and Poland, and has also branched out to the UK and France.
Those texted to say that they would be flying on Small Planet Airlines carriers were told: "The departure time, flight number and booking reference is the same. If you choose not to travel, we can offer you a full refund by contacting our Contact Centre by phone. Norwegian apologizes for the inconvenience."
Budget airline Norwegian is Scandinavia’s third-largest airline and has around 4,500 employees. Around 150 Swedish pilots work for the firm. Its parent company NAS is partly owned by subsidiaries in Sweden, Denmark, Finland, Ireland and Singapore.
Staff working for fellow Scandinavian airline SAS returned to work on Monday after a separate four day strike which led to dozens of cancelled and delayed flights in and out of the Danish capital over the weekend, a key hub for travellers moving on to Malmö and other cities in southern Sweden.