In accordance with the principle of legality, which is one of the most important basic principles of tax law, it is important that the essential elements of taxation is regulated by law. One of these elements is “durations” as it is generally accepted in the doctrine. In tax law, many durations have been determined for document regime. With the recent legislative amendment regarding the billing period, which is one of document regimes, the Ministry of Treasury and Finance has been authorized by the legislator to shorten the standard seven-day-period within the framework of various criteria. In this study, the authority given to the Ministry regarding the billing period is examined in terms of legal certainty and equality, which are constitutional principles, within the framework of opinions in literature and judicial decisions. When this mentioned authority is examined in detail, it has been concluded that it can lead to discussions in terms of legal certainty and equality principles. Within the scope of the study, it has been concluded that the authority given is controversial in terms of legal certainty and the principle of equality.