This accompanying EU regulation MiFIR requires the application for the Legal Entity Identifier LEI in article 26, paragraph 6.
MiFIR Regulation Article 26 Obligation to report transactions (extract)
1. Investment firms which execute transactions in financial instruments shall report complete and accurate details of such transactions to the competent authority as quickly as possible, and no later than the close of the following working day.
The competent authorities shall, in accordance with Article 85 of Directive 2014/65/EU, establish the necessary arrangements in order to ensure that the competent authority of the most relevant market in terms of liquidity for those financial instruments also receives that information.
The competent authorities shall make available to ESMA, upon request, any information reported in accordance with this Article. […]
3. The reports shall, in particular, include details of the names and numbers of the financial instruments bought or sold, the quantity, the dates and times of execution, the transaction prices, a designation to identify the clients on whose behalf the investment firm has executed that transaction, a designation to identify the persons and the computer algorithms within the investment firm responsible for the investment decision and the execution of the transaction, a designation to identify the applicable waiver under which the trade has taken place, means of identifying the investment firms concerned, and a designation to identify a short sale as defined in Article 2(1)(b) of Regulation (EU) No 236/2012 in respect of any shares and sovereign debt within the scope of Articles 12, 13 and 17 of that Regulation. For transactions not carried out on a trading venue, the reports shall include a designation identifying the types of transactions in accordance with the measures to be adopted pursuant to Article 20(3)(a) and Article 21(5)(a). For commodity derivatives, the reports shall indicate whether the transaction reduces risk in an objectively measurable way in accordance with Article 57 of Directive 2014/65/EU. […]
6. In reporting the designation to identify the clients as required under paragraphs 3 and 4, investment firms shall use a legal entity identifier established to identify clients that are legal persons. […]
The Legal Entity Identifier (LEI), referred to in the EU regulation MiFIR, is issued to the relevant legal entity by an accredited organisation known as Local Operating Units (LOU).