IANAL, nor in HR - but I'd assume that "directly related to their ability to perform the job" is the key. If you're hiring rocket scientists, I'd bet you could

IANAL, nor in HR - but I'd assume that "directly related to their ability to perform the job" is the key. If you're hiring rocket scientists, I'd bet you could ask 'em some tortuously difficult questions about rocket science. Or brain surgeons about brain surgery, or nuclear physicists about nuclear physics, or ...