IQ tests in employment are not illegal. This is an Internet myth. Several large corporations (with deep pockets for employment lawyers to go after) openly use them.

The reason more companies don't use IQ tests in candidate qualification is that they don't work well.

Where is an IQ test illegal? I remember taking one for my first job in Florida, but the company stopped because it wasn’t a useful signal.

IQ is correlated to many things (eg, income) but I’m not sure about job performance. Maybe for some industries. I was working for a software company and it seemed pretty useless for hiring or selecting project team members.