"... working illegally."
If it's illegal - arrest them, destroy their shops and ban them!
As far as I remember it was Thailand itself to invite and welcome them because they were supposed to boost the economy.
As long as Thai people could make a Baht out of them, they were regarded as a welcome victim.
No, when they take over Thai jobs, it's time to complain.
Get active and give a sh.... on the "good reputation"!