A strike that is not supported by the union is called a wildcat strike.
Since 1976, a wildcat strike is illegal if it takes place during a period when a collective agreement applies. If the strike is carried out during a period when there is no collective agreement, the support of the union is required so that the strike is not considered wild.
Wildcat strikes were more common in the 1970s and 1980s when many strikes were about local wage negotiations. Today, the possibilities for wage increases in addition to the central agreements are small and the wild strikes are also significantly fewer.
Wild strikes are now uncommon, the most recent was in 2017 when cleaning workers in Stockholm went on a wild strike over a new salary system.
The train drivers who are now on strike in the commuter train traffic risk having to pay damages if the employer goes to the Labor Court. According to those organizing the strike, it is about SEK 3,000 per person and strike occasion.
According to Christer Thörnqvist, docent in occupational science at the University of Skövde, however, they do not risk their employment.
Then the strike must have lasted a very long time. You don’t lose your job for a wild strike in three days.