Casting director. They're the ones with "C.S.A." at the end of their names at the credits of each movie. Like: Nina Gold, C.S.A. The union contract REQUIRES that 'c.s.a.' for members of the Casting Association of America lol.
When you see "ACE" that's an accredited union editor. Like John Doe A.C.E.
The unions are pretty nazi about the accreditation rules, but the film agents are actually the ones to push hard for them because they used to invalidate people for awards unless the credits were just so.