Swede here. Last time this happened was last year when the dock workers blocked the unloading off Russian ships. This proved to be illegal according Swedish labour law (reading strikes and blockades).

This is a slightly different situation since they are in fact having a “sympathy strike” which essentially is them supporting another union’s fight. The right is for the employer to sign an collective agreement. Since the are no minimum wage and other minimums in Swedish labour law such an agreement is a cornerstone for employers and employees in Sweden.