Well, while it's completely legal, it's not entirely by the book. It starts to get a bit of a gray area when you reach a certain size.
The unions, including the employer unions (NB!), have during the past century kept the country's lawmakers mostly out of regulating workforce agreements, including things like minimum pay, workplace insurance, and large parts of the pension system. These things are regulated by sector, and the regulations are re-bargained on a set schedule by these parties alone.
You can't stay out of these agreements for too long once you reach a certain size. The unions are trusted to handle this by their own. That is mostly done by sweetening the deal until it is accepted, usually by signing away the fundamental right to strike. It is not obvious if such fundamental rights really are bound to contract, especially not with the European Court, but it has resulted in a society where strikes are almost unheard of. Calling a strike without the backing of a union is pretty ineffective anyway, and the unions have their self interest in strong companies that can compete internationally and provide new jobs for the workforce.
The only times strikes are called are when some company will not present a counterparty to a contract negotiation, which is what this situation is. That happens once every decade and when it happens the unions all move in unison with several decades of money saved up, to show their might in order to make the affair as swift as possible. It's something that is often rehearsed often and seldom practiced.
Solidarity strikes are expected as a show of force. Things will escalate from there. While the part about an offer you can't refuse clearly has some similarities with mafia operations, the boundaries are clearly defined by law. There are lawyers specializing in this their entire careers.
Comparing this with the Chinese system misses the point by a mile.