Microsoft Terminal Server “User” CAL Question

In a Microsoft Terminal Server environment with CALs setup for per-user, can individuals share AD accounts to “beat” Microsoft’s licensing rules?

For example, if 100 users use the same account to login, does that count as 100 CALs or 1 CAL in a per-user CAL environment?

I ask this because my company has encountered a client that does this. I would think that he is breaking Microsoft’s TOS but I’m not sure. Thanks.