A goal of post-merger integration (PMI) is to combine several companies into one common entity so that Mergers and Acquisitions (M&A) strategic objectives can be achieved (some examples of objectives are growth, optimization, strength, etc.). As an integration process is related to large amounts of information to be acquired, processed, and applied during integration planning and execution phases, knowledge management can be perceived as one of the key supporting factors during the PMI. Additionally, although a PMI should cover integration of all system perspectives – social, cyber and physical; today, in many organizations, the main impact is on the cyber perspective, as it forms the infrastructure for the functioning of the whole system. This leads us to the assumption that the PMI process should be organized in such a way that information system integration becomes its central part including knowledge management activities. This research explores a requirements engineering model that can be incorporated into the PMI phase of any M&A initiative. In comparison with common requirements engineering approaches, this model extends them and is adjusted to support the following PMI features: (1) Focus on the integration and M&A strategic goals. (2) Extensive knowledge management with accumulating M&A experience, (3) Coverage of both explicit and tacit knowledge in all three system perspectives – social, cyber and physical.