I've heard that under EASA FI's should only work for one ATO
But that would undermine one of the objectives of EASA
Article 2
Objectives
1. The principal objective of this Regulation is to establish and
maintain a high uniform level of civil aviation safety in Europe.
2. Additional objectives are, in the fields covered by this
Regulation, as follows:
(b) to facilitate the free movement of goods, persons and
services;