It is, though, not a breach of the protocol that the Commission is complaining about in the article 258 proceedings.
This is because those powers given to UK ministers under the internal market bill have yet to be exercised. Instead, the Commission is complaining about a more general breach of article 5 of the withdrawal agreement on the duty of good faith.
Article 5 provides that the EU and UK must take “all appropriate measures, whether general or particular, to ensure fulfilment of the obligations arising from this agreement and shall refrain from any measures which could jeopardise the attainment of the objectives of this agreement”.
The Commission made clear its displeasure the day after the internal market bill was published. It said the UK government would be in violation of the good faith obligation as the “bill jeopardises the attainment of the objectives of the agreement”.
For good measure, the Commission said: “The EU does not accept the argument that the aim of the draft bill is to protect the Good Friday (Belfast) agreement. In fact, it is of the view that it does the opposite.”
In a direct rebuttal to Lewis, the Commission said that if the internal market bill were adopted this would constitute “an extremely serious violation of the withdrawal agreement and of international law” and the commission would not be “shy in using” the legal remedies in the text.
And so it has come to pass. During the transition period, which lasts until the end of the year, the Commission has the power under article 131 to apply existing EU remedies “as regards the interpretation and application of the agreement”. This includes the ability to start article 258 enforcement proceedings, the process used when a member state is in breach of EU law.
The Commission’s letter of formal notice, published yesterday, is the first phase. After a month, if the Commission is not satisfied with the UK’s answer, it can issue a reasoned opinion to which the UK would have two months to respond.
The Commission can ask the European court of justice for interim measures and to fast-track the case. But usually cases take about 12-18 months. If the court of justice finds against the UK it issues a declaration; a failure by the UK to remedy the breach would lead to further enforcement proceedings brought by the Commission and eventually a lump sum and/or penalty payment.
But this is all years away. The first two stages already take the UK to the end of December 2020. By then, we shall know whether there is a deal on the future trading relationship. So this feels more like politics than law.
But the EU is playing to its domestic audience too. Its own member states are breaching or threatening to breach the rule of law in other matters. It cannot be seen to be reprimanding them but taking no steps against the UK.
In short, Britain is threatening to breach the withdrawal agreement – and the EU is not taking this lying down.
By Catherine Barnard, senior fellow of UK in a Changing Europe and professor of EU law at Cambridge University. This piece was originally published by the Guardian.