They actually threatened him with an arrest, their explanation was that Smokey the Bear is "congressionally protected". How much weight it actually had is debatable, but Ward was notoriously squeemish about criticism. Bill Scott, however, was ready to fight them on it.
Something that's lost on today's audiences, and maybe even the audiences when this cartoon came out: blaming the Great Chicago Fire on Mrs. O'Leary (or her cow) was a way for whites to say, "fucking Irish ruin everything". (It was still some time before the Irish would be truly white.)