We consider the answer to the question of what an employer should take into account when he receives a letter regarding scope investigation from the collective bargaining parties or the industry pension fund and what consequences mandatory affiliation with a collective bargaining agreement and/or pension fund may entail. In addition, we talk about what steps an employer must take to adjust the terms of employment if mandatory affiliation follows. Thus, it deals with, among other things: retroactive affiliation, double pension accrual, prescription, the burden of proof, collective value transfer of pensions, changing terms of employment, etc.