There is much debate inside the EU at the moment about the rules that govern labour mobility. Macron wants to change these, the East European members want to keep present arrangements. The richer countries are finding their high wages undercut by cheap labour from the East.
However, if the EU is to integrate economically, there has to be free movement of labour and if a firm finds a competitive advantage it should be able to use it. This is the quickest route to an evening up within the continent. However, there are transitional problems since rich countries do not want to see wages squeezed. The only real way to avoid this would be for the rich countries to invest heavily in the poor ones, thus bringing their economic level up as quickly as possible. The solution is not restriction but expansion, but this requires expansion without regard to national boundaries. A more powerful central authority in Europe could make such regional priority more of a priority, but while national governments - even that of Macron, supposedly an arch-pro-EU - are busy defending national interests against continental ones this is going to be difficult to achieve.
Some of it is surely the nature of the system - a politician has to represent three levels - the people who voted for him as against the people who didn't; the whole constituency/country he represents versus other constituencies; and thirdly, the wider international interest. The interests and demands of these three levels often contradict each other.