Article I-19 (2) refers.
The Article sets out that the EU parliament should be composed of "representatives of the Union's citizens" and limits its size to 750 members.
Crucially, it then requires that "representation… shall be degressively proportional", with a minimum threshold of six MEPs per Member State. No Member State can have more than 96 seats.
This means that Malta, with a population of 380,000, and Luxembourg with 440,000 (approx) will each have six MEPs. On the other hand, the North East Region of England, with a population of 2.5 million, gets three. That is democracy, EU style.