Comment by jjk166

This is not a situation unique to after hours messages. The workplace is full of instances where an employer can discriminate against an employee in small but meaningful ways, you need robust employee protections, not a series of questionable legal hacks.

Replace responding slower with say being a different skin color. If a white and a black employee are equal on meaningful metrics but one gets to go on all the fun trips while the other is consistently given the shit tasks, that's obviously a problem, but you can't simply avoid the situation where the problem might present itself. You need structures in place so that employees can identify that they're being mistreated, notify someone with the power to fix the situation, confirm that the problem has actually been solved, and escalate if not; all without fear of retaliation. That is tough to do, but it doesn't make it any less necessary. Once you have that system in place, it is the logical way to deal with all forms of mistreatment. Then there is no need for special exceptions which substitute one rigid restriction for another.