For matters concerning the implementation of applicable EU law, standard EU procedures apply. 

According to Article 12(4) of the Protocol on Ireland/Northern Ireland, 'the institutions, bodies, offices, and agencies of the Union shall in relation to the United Kingdom and natural and legal persons residing or established in the territory of the United Kingdom have the powers conferred upon them by Union law.'

Infringement proceedings may therefore be brought against the UK. Ultimately the matter may be referred to the Court of Justice of the EU and a financial penalty applied. As the Protocol is part of EU law, it also falls under the scope of EU judicial review procedures. The legality of EU acts can also therefore be challenged if they are considered to be in breach of the Protocol.  

To date the EU has initiated infringement proceedings against the UK in relation to the Protocol on several occasions.

On the first occasion, the EU acted in response to the UK government tabling its UK Internal Market Bill and in doing so acknowledging it would be in breach of its obligations under the Withdrawal Agreement. The European Commission issued a first letter of formal notice on 1 October 2020. With the UK eventually removing the offending clauses from the UK Internal Market Bill, the proceedings against it were dropped. The second occasion was in response to the UK non-implementation of applicable EU law relating to the free movement of goods and pet travel. A second letter of formal notice was issued on 15 March 2021. 

Several months later, in July 2021 the EU paused the two infringement proceedings against the UK for non-implementation of the Protocol to create "necessary space" for talks. Following the UK government's introduction of draft legislation that would see key elements of the Protocol disapplied in domestic law, the EU relaunched its two existing infringement proceedings against the UK and began a third case on 15 June 2022. 

Most recently, on 22 July 2022, the EU launched four new infringement procedures against the UK for failure to implement or fulfill obligations that arise under the Protocol and those EU laws it makes applicable to the UK in respect of Northern Ireland. The four procedures concern: failure to comply with applicable customs requirements, supervision requirements and risk controls on the movement of goods from Northern Ireland to Great Britain; failure to notify the transposition of EU legislation laying down general EU rules on excise duties; failure to notify the transposition of EU rules on excise duties on alcohol and alcoholic beverages; failure to implement EU rules on VAT for e-commerce, in particular the Import One-Stop Shop (IOSS) scheme. The UK government must formally respond to these latest infringement proceedings by 15 September 2022, or seek an extension for the same purpose.