It’s pretty simple, crew who hold greencards have been lying about it to the company and the IRS. They avoid paying US tax but the company gets fined big time when the IRS finally connects the dots............as the IRS usually does.
They then get in strife with the company, who isn’t happy about paying the IRS big fines. The AOA gets involved, “they only lied, you only got fined, no harm done” etc.
Pilots and tax, this sh*t never gets old......