Social labour inspectorate, as a special form of unionised representation of employees’ interests, has the right to control employers in the field of their compliance with the provisions of the labour law in place. Exercising this controlling function involves the need for a social labour inspector to access the information and docu-ments that may contain personal data of employees. The study advances a thesis that a social labour inspector is an entity processing personal data of employees on behalf of a company trade union organisation – who is the controller of these data, and the grounds for the processing of personal data of employees are the relevant provisions of the GDPR. The theses proposed in the study aim to challenge the Constitutional Tribunal’s standpoint regarding a social labour inspector’s right to obtain personal data. The problems addressed in the study have not been a sub-ject of the existing views of legal academics and commentators, nor have they been covered in the established line of judicial decisions yet.