That's called double billing and is considered unethical [0]:
> In law, double billing refers to charging an hourly rate to two clients for the same time spent working. The American Bar Association prohibits double billing. It is tantamount to overcharging, since the amount of time actually spent working on any one client's work is less than the amount billed to that client.
> In law, double billing refers to charging an hourly rate to two clients for the same time spent working. The American Bar Association prohibits double billing. It is tantamount to overcharging, since the amount of time actually spent working on any one client's work is less than the amount billed to that client.
[0] https://en.wikipedia.org/wiki/Double_billing