The EORI number is obligatory for companies engaged in foreign trade in exporting, importing, transit and other customs operations.
The Economic Operators Registration and Identification (EORI) system was set up to implement security measures. Security measures are more effective if the persons concerned can be identified by a single number which is unique for each individual and valid throughout the community.
In Estonia, the EORI code is issued by the Estonian Tax and Customs Board.
Additional information: http://www.emta.ee/et/ariklient/toll-kaubavahetus/ettevotja-registreerimine-eori