Unions don’t stop lay-offs, but this is still a strong move and probably the most likely to succeed. CDPR needs to find new income now that they don’t have a game on the horizon, so they need devs to produce.
Literally, the power is in the devs’ hands here. CDPR's only option is to either work with the union or lay them all off and then not release any new products and go bankrupt.
Hopefully, it spreads to more European countries and becomes normal business for games to be made with unions in Europe