The purpose of the study is to discuss the issues related to the status of a shareholder in a limited liability company (spółka z ograniczoną odpowiedzialnością, "sp. z o.o.") with particular emphasis on the shares held in the company in relation to the change of circumstances triggering the obligation to pay compulsory social insurance under Article 6(1)(5) in conjunction with Article 8(6)(4) of the Act on Social Insurance System of 13 October 1998 (hereinafter: system act).The above issue is important because this issue is currently the subject of consideration by the Supreme Court in the case ref. no. III UZP 8/23 (date of receipt: 17 October 2023) where a legal issue arose that will ultimately answer the following question: "is a shareholder of a two-person limited liability company holding 99 percent of shares that give him the ability to freely shape the content of resolutions at the meeting of shareholders and make decisions regarding the company's activities, subject to social insurance pursuant to Article 6(1)(5) in conjunction with Article 8(6)(4) of the Act on Social Insurance System of 13 October 1998?" Therefore, in this study the author will attempt to answer the above legal issue by interpreting the relevant provisions of the law relating to the described issue.

The aim of the study is to discuss the issues related to the possibility of applying the prohibition to reformationis in peius before medical certification bodies in proceedings before the social security organ. The subject matter of the issue in question is important because it shows the de facto existence of a universally accepted position, along with some discrepancies that arose as a result of creating an atypical line of jurisprudence by some judicature, which is a kind of novelty regarding the examination of the issue in question. Therefore, the article discusses the impact of the functioning of the above-mentioned institution, with the content currently in force, on the essence of proceedings before the social security organ, and presents an approximation of the general characteristics of the prohibition of reformationis in peius in relation to the relevant provisions of the Code of Administrative Procedure, as well as the so-called retirement-social security acts.