There is debate over just how important these words are. Sir William Cash, a Conservative MP, said last month that:
"even if the words 'ever-closer union' were removed from treaties in the future, it would not change any of our existing EU obligations and laws, nor fundamentally change our relationship with the EU under the existing treaties".
But David Cameron replied that "this concept does have legal force because ever-closer union has been used by the courts to enforce centralising judgments".
We've covered that issue in a recent factcheck, concluding that the phrase has little direct legal effect, although it's been argued that it provides the EU Court of Justice with an overriding sense of mission toward further European integration. The impact of its removal would be mainly political.
That doesn't mean it would be unimportant, but Sir William is right that no existing EU obligations or laws would disappear if the UK were no longer associated with ever closer union.
One additional point to make on the politics of the concept is that EU governments declared last year that it doesn't mandate a political drive towards one-size-fits-all integration.
The European Council said in June 2014 that:
"the concept of ever closer union allows for different paths of integration for different countries, allowing those that want to deepen integration to move ahead, while respecting the wish of those who do not want to deepen any further".