I'm in Sweden, where most people are in a union. It doesn't have to be a union specific to game development (although I think one may exist, I'm not sure). I'm in a general union called Unionen. Even though it's not a union specific to the game development industry, they have a lot of power and work with the government, companies, and employees to monitor and improve work conditions and employee protections. For example, last year a series of meetings was held at our workplace between interested employees and union representatives, resulting in a new collective bargain agreement which formalised a flex hours policy and gave us an extra paid week off per year (partly to address the overtime we tend to do). I've heard of cases where employees called in their union representative to help them work through issues with the employer, negotiate better termination agreements, etc. Basically it's a normal union that does union-y things :)

In Finland at least game devs fall under some general IT collective bargaining agreement, so they have union presentation but it's more general software/IT. Works decently. From my experience the games industry is a bit too... wild(?) to really think about things like unions by itself.