French president Macron has recently caused controversy with his contrast of extra-EU legal immigration and intra-EU illegal movements of EU/EUAA people:

Last week, the right-wing French magazine Valeurs Actuelles published an interview with Macron who said he favored legal quota-based migration to illegal workers, contrasting Guinean or Ivorian migrants who work legally to "clandestine gangs of Bulgarians and Ukrainians."

(Macron also recently opposed further EU enlargement in the Balkans.)

Are illegal movements of EU citizens in the EU a significant problem? E.g. is there a significant black market for Eastern EU labor in the West, for instance in prostitution, undeclared day labour, and similar? Are there any estimates for the magnitude of these phenomena? Likewise, are there similar estimates for the EU-associated countries like the Ukraine?