On the other hand, IQ was one of the direct methods of discrimination used in the flagship case establishing the doctrine of adverse impact discrimination (leading to a popular myth that IQ discrimination is itself entirely illegal), and the cases where IQ discrimination (high or low) in employment has been found to not be illegal have invariably involved the employer presenting the kind of business necessity evidence needed to overcome the presumption of adverse impact discrimination that occurs when discrimination has a negative differential impact on a protected class without direct targeting, so discrimination based on IQ (or, for the same reason, factors indirectly associated with IQ that don't happen to completely negate the negative differential impact without transferring it to a different protected class) isn't generally legally safe even though it isn't directly prohibited.
On the other hand, IQ was one of the direct methods of discrimination used in the flagship case establishing the doctrine of adverse impact discrimination (leading to a popular myth that IQ discrimination is itself entirely illegal), and the cases where IQ discrimination (high or low) in employment has been found to not be illegal have invariably involved the employer presenting the kind of business necessity evidence needed to overcome the presumption of adverse impact discrimination that occurs when discrimination has a negative differential impact on a protected class without direct targeting, so discrimination based on IQ (or, for the same reason, factors indirectly associated with IQ that don't happen to completely negate the negative differential impact without transferring it to a different protected class) isn't generally legally safe even though it isn't directly prohibited.