It starts from the top. First of all, in such structures such companies does not pay 3 items that is suppose to be paid to the tax office.
1st- Income tax 2nd-Social Security Contributions 3rd-Health Related premiums. Employees of such companies mostly does not pay any of those neither. First of all companies make a lot of profit by doing this. Imagine a airlines paying legal pay to its pilots. Lets say, captain salary is about 9.000 Euros net p/m, to receive this net amount in your bank account cost to the airlines is approximately 16.000 Euros in western EU countries. This amount of 7.000 euros in between is pure profit for airlines and they are making it on your shoulders.
Of course ACMI salary of 9.000 for captain is in reality is gross amount, and we are still not realising how much money we are losing and how we are helping those ACMIs to make money,
As a result, ACMI company evading tax from its tax office, which is complete illegal. Second of all, they are not paying social security contribution which is breach of labor law and labor rights.
Pilot job cannot be contracting job, we cant work for more than 1 airline in reality. In anywhere around the world if you do contracting job you receive much more than directly employed person therefore you can make these contribution to the state by yourself.