I haven't been able to find a particularly clear answer to this question. If I'm a non-US employer (no physical presence in the US and the main money-making personal services are performed outside the US), do I have to withhold the employer half of US employee FICA tax for any US employees residing in the US? If I was a US-based employer the answer would of course be "yes" but I haven't seen a clear direction for non-US employers.
I've seen that for US employees, they are always subject to withholdings for income tax and FICA, but I can't seem to find anything about the employer half.