On 1 June 2017, following an amendment to the Code of Administrative Procedure, the possibility to file a statement on waiving the right to appeal was introduced. In consequence – as of the date of serving the public administration authority with the statement of waiver by the last of the parties to the proceedings – the decision becomes final and legally binding. However, it is assumed by legal scholars and commentators and in the established line of judicial decisions that the right to file an appeal against a decision issued in the course of administrative proceedings extends not only to the parties that participated in the proceedings and were served the decision, but also to an entity which was not considered a party by the first instance authority, provided that the entity meets the statutory criterion of obtaining the status of a party to proceedings. The time limit for filing an appeal by the non-participating entity runs from the date of serving or communicating orally the decision to the parties to the proceedings, and in case the decision was served on different dates to more than one party – from the last date of serving the decision. With regard to the legal effect of the waiver of appeal, whereby the first instance decision becomes final and binding, a question arises as to how the waiver affects the possibility to file an appeal, within the original time limit, by an entity which was not considered a party to proceedings by the authority. The paper seeks to answer this question.