Getting Entities whose keys match list(or array) of ids

I am using CodeFirst EntityFramework. I have a IQueryable<User> Entities that are returned using context.Users; where context is DbContext of EntityFramework. From this list I have to choose those whose Id is contained in an array of Ids (long). Id is primary key of User entity. I have tried the following but getting compiler error.

IQueryable<User> users = GetQueryableUsers(); 
long [] ids = GetSelectedIds(); //array of long representing Ids key of User entities
users.Intersect(ids); // compilation error
users.Where(user => ids.Contains(user.Id)); //compilation error

Compilation error is (no definition found for Intersect/Contains) Note: System.Linq is already imported.