Commission Implementing Regulation 2022/1203/EC added 22 invasive alien species of Union concern (IAS of UC) to the Union List set under EU Regulation (EU) 1143/2014 (IAS Regulation). IAS of UC are alien species whose adverse impact has been deemed so severe to require concerted action at Union level. Towards this aim, high-quality and updated data on the new IAS of UC is crucial for their management. This report provides the baseline distribution of 13 IAS of UC out of 22 added to the Union list, which are currently present in the EU territory and to which the IAS Regulation applies. This data constitutes the reference baseline at European level. 18 EU Member States (MS) Competent Authorities contributed to the definition of the baseline by revising and supplementing spatial data harvested from the European Alien Species Information Network (EASIN). In addition to the species spatial distribution for each IAS of UC, the report contains information on the taxonomic group, origin, first introduction in the EU, main pathway of introduction in the EU, habitat, and ecosystems impact. To this end, the pressure caused by the 13 IAS of UC on terrestrial and freshwater ecosystems across the EU is assessed in this report. Results show that 77% of these IAS of UC are from the Kingdom Animalia and the Infraclass Teleostei (31%). 50% of freshwater and terrestrial IAS of UC were introduced in Europe through the primary pathway "Escape from confinement" and 20% by intentional introductions: "Biological control" (10 %) or "Other intentional release" (10%). The distribution of the 13 species subject of the baseline shows their highest number of established occurrences in France and Spain, i.e., 8 and 7 respectively, and the lowest in Denmark, Luxemburg, Sweden and Slovakia. Six species are more frequent across EU: Ameiurus melas, Gambusia holbrooki, Koenigia polystachya, and Gambusia affinis. Croplands ecosystems show the highest percentage of invaded area and the highest average of cumulative pressure by IAS of UC, suggesting negative impacts on agroecosystems. On the opposite side, the lowest pressure is recorded in grassland areas. This baseline will support MS in the implementation of the IAS Regulation. It will help adapting the surveillance and monitoring systems and is an essential reference to the application of "Early detection Notifications" and will also support the review of the IAS Regulation. In addition, this data is key for fostering MS cooperation and coordination across borders or within shared biogeographical regions.