The Union Registry allows account holders to distinguish international credits that are eligible in the EU ETS from those not eligible (ineligible).

This functionality of the Union Registry implements the rules related to the holding of certain units on EU ETS accounts in 2013 - 2020.

According to the Regulation 2019/1122, which will be effective from 1 January 2021 and regulates the functioning of the Union Registry in the 4th trading period, it will no longer be possible to use international credits (CER, ERU) in the EU ETS in the 4th trading period. After 30 April 2021, the entitlements to exchange these credits will expire and it will not be possible to transfer these units between EU accounts. They can be held on these accounts until 1 July 2023. Until that date, credits must be transferred to the Kyoto Protocol accounts.

List of installations with remaining entitlement.
The status is as of 13 January 2021.

International credits CERs and ERUs may be identified as:

Eligible

• also known as green,
• applicable for the trading period 2013 - 2020,
• may be hold on EU accounts until 1 July 2023,
• may be transferred between accounts without any restrictions,
• their exchange for allowances is available on a one-to-one basis. Exchange of eligible Kyoto units for allowances is available from 28 Mach 2014 in the registry. Instructions for Exchange can be found here (only in Czech version).
  This exchange is available to operators or aircraft operators up to their entitlement, which is determined by Commission Regulation (EU) no. 1123/2013 on determining international credit entitlements (the wording is here).
  This exchange is available until 1 May 2021.
• cannot be directly surrendered instead of allowances anymore.

Ineligible 

• also known as grey,
• these international credits cannot be used in the EU ETS, so they cannot neither be held in the EU accounts nor be transferred to these EU accounts,
• they must be cancelled or transferred outside the EU accounts to the Kyoto Protocol accounts (CZ accounts).

You may find more information about use of international credits here.

Lists published by the European Commision (General positive list, Specific positive list, General negative list), which determine the eligibility / ineligibility of international credits under applicable legislation are available here.