Answer to this question depends on what you mean.
If your refer to a certificate issued for multiple attorneys, it is for sure a "power of attorneys"
But if you, as often, refer to multiple documents, each of which appoint an attorney, they are called "powers of attorney".
Let me also note that using the term PoA (and "PoA's" for the plural form) is a nice way to get around this doubt, considering both answers above sound unfamiliar in fact.
If your refer to a certificate issued for multiple attorneys, it is for sure a "power of attorneys"
But if you, as often, refer to multiple documents, each of which appoint an attorney, they are called "powers of attorney".
Let me also note that using the term PoA (and "PoA's" for the plural form) is a nice way to get around this doubt, considering both answers above sound unfamiliar in fact.
