It is not illegal to use IQ tests as part of a job screening (in the US). It is illegal to screen in a way that is both discriminatory and not proven to correlate with job performance, but that applies equally to both IQ tests and algorithms questions.

IQ is proven to correlate with performance in virtually everything, so I'm not sure where you're going with that.

If I require all prospective engineering hires to prove explicitly that they have an IQ of at least 135, I will get sued. Do you think this is false?

Obviously I do not think that is false; you can get sued for literally anything. Do I think you would lose? Depends on whether you've done the research showing that 135 is an important cut-off.

To turn this around, can you point at the law that makes IQ a protected class or whatever you're claiming it is? I'm not going to have much luck proving a negative - Russell's teapot and all that.