A recent Ontario decision explained why employer references are treated somewhat differently by libel laws: 

"The social policy underpinning the protection of employment references in this manner is clear: an employer must be able to give a job reference with candour as to the strengths and weaknesses of an employee, without fear of being sued in defamation for doing so. Without this protection, references would either not be given, or would be given with such edited content as to render them at best unhelpful or at worst misleading to a prospective employer."

~  Kanak v Riggin, [2017 ONSC]